Learn Hardcore German: Wenn ich an mir zweifle, erinnert mich meine Freundin an meine Erfolge. - When I doubt myself, my girlfriend reminds me of my successes.

an + Dativ after zweifeln
- an mir zweifeln = to doubt myself
- an dir zweifeln = to doubt you
- an ihm / ihr zweifeln = to doubt him / her

So the correct forms are:

ich zweifle an mir (not an mich)
ich zweifle an dir (not an dich), etc.

The pattern is:

zweifeln an + Dativ

Why does the verb go to the end in Wenn ich an mir zweifle?

Wenn is a subordinating conjunction. In German, subordinating conjunctions send the finite verb to the end of the clause.

Structure:

Wenn
- subject + (objects / adverbs) + verb at the end

In your sentence:

Wenn – subordinating conjunction
ich – subject
an mir – prepositional object
zweifle – verb, goes to the end

So:

Wenn ich an mir zweifle, … (correct)
Wenn ich an mir zweifle, erinnert mich meine Freundin an meine Erfolge.

The second part (erinnert mich meine Freundin …) is a main clause, so there the verb is in normal second position.

What is the difference between wenn and als here? Could I say Als ich an mir zweifle?

You cannot use als in this sentence with the same meaning.

Basic rule:

wenn
- for repeated or general situations (whenever / if)
- also for future conditions
als
- for a single event in the past (one specific time)

Your sentence expresses a general, repeated situation:

Whenever / if I doubt myself, my girlfriend reminds me of my successes.

So wenn is correct:

Wenn ich an mir zweifle, erinnert mich meine Freundin an meine Erfolge.

Als would only work for something like:

Als ich an mir zweifelte, erinnerte mich meine Freundin an meine Erfolge.
= That one time in the past when I doubted myself, my girlfriend reminded me of my successes.

Here it’s clearly a general habit, so wenn is the right choice.

Why is it erinnert mich and not something like erinnert sich mich?

There are two related structures with erinnern:

jemanden an etwas erinnern (active, non‑reflexive)
- someone reminds someone of something
- pattern: Subjekt + erinnert + Akkusativobjekt + an + Akkusativ
Example:
- Meine Freundin erinnert mich an meine Erfolge.
  - Meine Freundin = subject (who does the reminding)
  - mich = direct object (who is reminded)
  - an meine Erfolge = what I’m reminded of
sich an etwas erinnern (reflexive)
- someone remembers something
- pattern: Subjekt + erinnert sich + an + Akkusativ
Example:
- Ich erinnere mich an meine Erfolge.
  - Ich = subject
  - mich = reflexive pronoun (same person as the subject)

In your sentence, the girlfriend is doing the reminding, so we use pattern 1 (non‑reflexive):

Meine Freundin erinnert mich an meine Erfolge.

If you said:

Ich erinnere mich an meine Erfolge.

then you are remembering your successes yourself (no one else reminding you).

Why is it an mir (dative) but an meine Erfolge (accusative)? Isn’t it the same preposition an?

Yes, it’s the same preposition an, but different verbs control different cases:

zweifeln an + Dativ
- pattern: an + Dativ
- an mir, an dir, an ihm, an ihr, an uns, etc.
  Example:
- Ich zweifle an mir.
- Viele Leute zweifeln an sich selbst.
jemanden an etwas erinnern uses an + Akkusativ
- pattern: jemanden an + Akkusativ erinnern
- an meinen Erfolg, an meine Erfolge, an dich, an diese Zeit, etc.
  Example:
- Sie erinnert mich an meine Erfolge.

So:

an mir → dative, because of zweifeln an + Dativ
an meine Erfolge → accusative, because of (jemanden) an + Akkusativ erinnern

The preposition an itself can take dative or accusative, but the verb decides which one you need in each expression.

Could I say Wenn ich an mir zweifle, erinnert meine Freundin mich an meine Erfolge instead?

Yes, that is also grammatically correct:

Wenn ich an mir zweifle, erinnert meine Freundin mich an meine Erfolge.

Both versions are possible:

… erinnert mich meine Freundin an meine Erfolge.
… erinnert meine Freundin mich an meine Erfolge.

Difference:

In version 1, mich comes right after the verb, which is very natural, especially when the subject is a noun phrase (meine Freundin).
In version 2, the word order is more neutral: subject → verb → object.

In spoken German, it’s very common to put short pronouns (like mich, dir, ihn) early in the clause, often directly behind the verb:

Sie erinnert mich immer daran.
Er hat mir gestern geholfen.

So the original sentence is slightly more idiomatic, but your version is absolutely correct and natural.

Why is there a comma before erinnert?

German must use a comma between a subordinate clause and the main clause.

Your sentence consists of:

Subordinate clause (with wenn):
- Wenn ich an mir zweifle, …
Main clause:
- … erinnert mich meine Freundin an meine Erfolge.

Rule:

After a wenn‑clause (or any subclause introduced by dass, weil, obwohl, als, ob, etc.), you always put a comma before the main clause.

So the comma in:

Wenn ich an mir zweifle, erinnert mich meine Freundin an meine Erfolge.

is not optional; it’s required by German punctuation rules.

Does meine Freundin always mean “my girlfriend” (romantic partner), or can it mean just “my female friend”?

meine Freundin can mean both, depending on context:

my girlfriend (romantic relationship)
my (female) friend (platonically)

In everyday conversation, meine Freundin often implies a romantic partner, especially if nothing else is said. To make it clearly non‑romantic, people sometimes add:

eine gute Freundin von mir – a good (female) friend of mine
meine Bekannte – my acquaintance
meine Kollegin – my (female) colleague

In writing or with context, it can be clear either way. Grammatically, it just means “female friend.”

Could I just say Wenn ich zweifle instead of Wenn ich an mir zweifle? What’s the difference?

You could say Wenn ich zweifle, and it is grammatically correct, but the meaning is less specific.

Wenn ich zweifle = when I doubt / when I have doubts (about something in general)
Wenn ich an mir zweifle = when I doubt myself (my abilities, worth, etc.)

So an mir adds the nuance that you are doubting yourself personally, not just doubting a plan, an idea, a fact, or something else.

Similar options:

Wenn ich an mir selbst zweifle, … – emphasizes “myself” even more
Wenn ich an meinen Fähigkeiten zweifle, … – when I doubt my abilities

What is the difference between zweifeln and bezweifeln? Could I say Wenn ich mich bezweifle?

zweifeln and bezweifeln are related but used differently.

zweifeln an + Dativ
- to have doubts about something / someone
- pattern: zweifeln an + Dativ
  Examples:
- Ich zweifle an mir. – I doubt myself.
- Ich zweifle an seiner Ehrlichkeit. – I doubt his honesty.
bezweifeln + Akkusativ
- to doubt something (more direct, like “to dispute”)
- pattern: etwas bezweifeln (accusative object)
  Examples:
- Ich bezweifle das. – I doubt that.
- Ich bezweifle seine Geschichte. – I doubt his story.

You normally do not say mich bezweifle; that sounds wrong. For doubting yourself, German uses an mir zweifeln (or an mir selbst zweifeln).

So:

Correct: Wenn ich an mir zweifle, …
Not natural: Wenn ich mich bezweifle, …

Why is the present tense used (zweifle, erinnert) if this can also refer to the future?

German present tense (Präsens) covers:

the present
regular or general truths / habits
the near future (in many cases)

Your sentence describes a general pattern or habit, not a single moment:

Whenever / If I doubt myself, my girlfriend reminds me of my successes.

For this kind of timeless or habitual statement, German uses the Präsens:

Wenn ich an mir zweifle, erinnert mich meine Freundin an meine Erfolge.

You could make it past or future if you want to change the time reference:

Past:
- Wenn ich an mir zweifelte, erinnerte mich meine Freundin an meine Erfolge.
  (describes a habitual situation in the past)
Explicit future (less common here, but possible in other sentences):
- Wenn ich zweifeln werde, … – sounds unnatural; normally you still use Präsens for future in such conditionals.

So the present tense is exactly right for a general, ongoing pattern.

What is the plural Erfolge vs. the singular Erfolg, and could I use the singular here?

Erfolg means success.

Singular: der Erfolg – one success, success in general
Plural: die Erfolge – several individual successes

In your sentence:

meine Erfolge suggests several specific successes (exams passed, projects completed, etc.).

You could say:

… erinnert mich meine Freundin an meinen Erfolg.

That would usually mean:

my (overall) success
or one particular success (context decides)

Both are grammatically correct; Erfolge just emphasizes multiple concrete successes that she reminds you of.