Learn Hardcore Portuguese (Portugal): Às vezes falta-me motivação, mas lembro-me de como tenho melhorado. - Sometimes I lack motivation, but I remember how I have been improving.

Falta-me motivação = Motivation is lacking to me (I lack motivation).
Me falta motivação is possible but sounds marked/poetic or more typical of Brazilian Portuguese everyday speech.

So for neutral, standard European Portuguese, falta-me motivação is the natural word order.

What exactly does faltar mean here, and how is falta-me motivação different from não tenho motivação?

Faltar literally means to be missing / to be lacking.

Falta-me motivação = Motivation is lacking to me → I lack motivation / I’m short of motivation.
Não tenho motivação = I don’t have motivation.

They often overlap in meaning, but:

Faltar sounds a bit more like something ought to be there but isn’t, or is not enough.
Não ter is more neutral possession/non-possession.

In this sentence, falta-me motivação sounds very idiomatic and natural for talking about motivation, energy, patience, money etc.:

Falta-me paciência. – I lack patience.
Falta-me tempo. – I don’t have enough time.

Why is there no subject eu before falta-me or lembro-me?

In Portuguese, subject pronouns (eu, tu, ele, etc.) are usually omitted when the verb form already makes the subject clear.

(Eu) falta-me motivação → falta-me motivação
(Eu) lembro-me… → lembro-me…

You normally add eu only to emphasize contrast, e.g.:

Às vezes falta-me motivação, mas eu lembro-me de como tenho melhorado.
(Sometimes I lack motivation, but I remember how I’ve been improving – stressing that I remember, maybe unlike others.)

Why is there an accent in Às vezes? What’s the difference between as vezes and às vezes?

Às is a (preposition) + as (feminine plural article) contracted, with a grave accent: a + as → às.

Literally, às vezes means at the times, but together it’s an idiomatic adverb meaning sometimes.

Às vezes (with accent) = sometimes.
as vezes (without accent) would just be the times (as a noun phrase), and is not used with this meaning.

Other ways to say sometimes in European Portuguese:

de vez em quando
por vezes (a bit more formal).

Why is it lembro-me and not just lembro? What does the -me add?

Portuguese has two related verbs:

lembrar – to remind (someone else) / to bring to mind
lembrar-se (de) – to remember

When you talk about remembering something yourself, you normally use the reflexive form lembrar-se:

Lembro-me de como tenho melhorado. – I remember how I’ve been improving.
Lembro-te disso. – I remind you of that.

So -me here is the reflexive pronoun (myself), and lembrar-se de = to remember.

Could I say mas eu me lembro instead of mas lembro-me?

That word order (eu me lembro) is typical of Brazilian Portuguese.

In European Portuguese:

The neutral form is lembro-me (pronoun after the verb).
Eu lembro-me is also correct, with a bit of emphasis on eu.
Eu me lembro sounds clearly Brazilian.

So for Portugal, you should stick to:

mas lembro-me de como tenho melhorado
or
mas eu lembro-me de como tenho melhorado (if you want to stress eu).

Why do we need de in lembro-me de como tenho melhorado?

The verb lembrar-se is normally followed by de when introducing what is remembered:

Lembro-me de ti. – I remember you.
Lembro-me de quando era criança. – I remember when I was a child.
Lembro-me de como tenho melhorado. – I remember how I’ve been improving.

So de is required by the verb lembrar-se; it links the verb to the clause introduced by como.

Without de, Lembro-me como tenho melhorado is possible in some contexts but sounds less standard; lembrar-se de is the safer pattern to learn.

What tense is tenho melhorado, and how is it different from just melhorei?

Tenho melhorado is the pretérito perfeito composto, which in European Portuguese usually corresponds to English have been doing (repeated or continuous up to now):

Tenho melhorado. – I have been improving / I’ve been getting better.

It suggests an ongoing process with repeated or continuous improvement up to the present.

Melhorei (pretérito perfeito simples) is more like English I improved / I got better (a finished event, seen as complete):

Lembro-me de como melhorei. – I remember how I improved (at some point / over a finished period).
Lembro-me de como tenho melhorado. – I remember how I’ve been improving (and this improvement is still relevant/ongoing).

Could I say tenho vindo a melhorar instead of tenho melhorado? Is there a difference?

Yes, you can say both:

tenho melhorado
tenho vindo a melhorar

Both can translate roughly as I have been improving, but there’s a nuance:

tenho melhorado is more compact and very common.
tenho vindo a melhorar often emphasizes a gradual, step-by-step progression over time.

In your sentence, both are acceptable and natural:

…lembro-me de como tenho melhorado.
…lembro-me de como tenho vindo a melhorar. (slight extra focus on the gradual process).

Why is there no article before motivação? Would falta-me a motivação be wrong?

Falta-me motivação is treating motivação as an uncountable/abstract quality, like patience, courage, energy. In this sense, you usually do not use the article:

Falta-me motivação. – I lack motivation.
Falta-me paciência. – I lack patience.

Falta-me a motivação is grammatically correct but sounds more specific, like referring to a particular/known kind of motivation, or maybe the motivation that I used to have. It’s less neutral and more context-dependent.

For the general statement in your sentence, falta-me motivação is the natural choice.

Is the comma before mas necessary?

In European Portuguese writing, you normally do place a comma before mas when it links two clauses, just as you often do before but in English:

Às vezes falta-me motivação, mas lembro-me de como tenho melhorado.

So yes, in standard written Portuguese this comma is expected, because mas is joining two independent clauses with their own verbs (falta and lembro).

Could I change the word order to Às vezes a motivação falta-me? Does it sound natural?

Yes, Às vezes a motivação falta-me is grammatically correct and can be used.

Differences in feel:

Às vezes falta-me motivação is more idiomatic and slightly more neutral.
Às vezes a motivação falta-me puts a bit more emphasis on a motivação as the topic: As for motivation, sometimes it fails me.

Both are acceptable in European Portuguese; the original version is probably the most commonly used.