Learn Hardcore Spanish (Spain): No estoy seguro de la respuesta, pero no me siento tan preocupado porque realmente he estudiado. - I am not sure of the answer, but I do not feel so worried because I have really studied.

Estoy seguro = I’m sure (right now / about this particular thing).
Soy seguro would mean something like I am a safe/reliable person (almost never used this way in practice; you’d more often say soy una persona segura or soy muy seguro de mí mismo = I’m very self‑confident).

In this sentence, not being sure about an answer is clearly a temporary state, so estar is correct:
No estoy seguro de la respuesta… = I’m not sure about the answer…

Why is there no yo in No estoy seguro de la respuesta?

In Spanish, verb endings already tell you who the subject is, so subject pronouns (yo, tú, él…) are usually optional:

Estoy already means I am.
Yo estoy is grammatically fine but adds emphasis, like I am not sure (maybe others are).

So:

No estoy seguro de la respuesta (neutral, most natural).
Yo no estoy seguro de la respuesta (emphatic I).

Why is it seguro de la respuesta and not seguro sobre la respuesta?

With seguro in the sense of “certain / sure”, the normal pattern is:

estar seguro de + noun / infinitive / clause

Examples:

Estoy seguro de la respuesta. – I’m sure of the answer.
Estoy seguro de haber aprobado. – I’m sure I’ve passed.
Estoy seguro de que vendrá. – I’m sure (that) he’ll come.

You can sometimes see seguro sobre, but it’s less idiomatic and sounds off in this context. Seguridad sobre la respuesta also sounds strange; seguridad en la respuesta is possible but different structure.

So here, de is simply the preposition that goes with estar seguro.

Why do we say la respuesta and not just respuesta without an article?

Spanish uses definite articles (el, la, los, las) more often than English.

la respuesta = the answer (a specific answer you both know about: e.g. test question 3).
Bare respuesta (no article) would feel incomplete here and is mostly used in set expressions or very abstract/general contexts, e.g. Respuesta correcta: on a worksheet.

Since we’re talking about a particular answer, Spanish naturally uses la respuesta.

What’s the difference between sentir and sentirse? Why is it no me siento tan preocupado?

sentir (non‑reflexive) = to feel something (an object):
- Siento frío. – I feel cold.
- Siento miedo. – I feel fear.
- Siento dolor. – I feel pain.
sentirse (reflexive) = to feel (oneself) + adjective/adverb:
- Me siento bien. – I feel well.
- Me siento cansado. – I feel tired.
- No me siento tan preocupado. – I don’t feel so worried.

In this sentence the structure is (no) + me siento + adjective, so we need the reflexive form sentirse: me siento.

What’s the difference between no me siento tan preocupado and no estoy tan preocupado?

Both are correct and very close in meaning:

No me siento tan preocupado.
Focuses slightly more on your subjective feeling: I don’t feel that worried.
No estoy tan preocupado.
Describes more your state/condition: I’m not that worried.

In everyday speech they’re almost interchangeable. Sentirse tends to highlight internal perception a bit more, but it’s a nuance, not a big grammar difference.

Why is it tan preocupado and not tanto preocupado or muy preocupado?

tan is used before adjectives and adverbs to mean “so / that / such” (in degree):

tan + adjective/adverb
- tan preocupado – so/that worried
- tan cansado – so tired
- tan rápido – so fast

tanto usually goes with nouns or by itself:

tanto + noun – so much/many
- tanto trabajo – so much work
- tantas preguntas – so many questions

So:

tan preocupado (correct: so/that worried).
tanto preocupado is wrong here.

You could also say no me siento muy preocupado (I don’t feel very worried), but tan suggests more of a comparison or a degree you might have expected to be higher: not as worried as you might think.

Why is it preocupado and not preocupada or preocupados?

Adjectives like preocupado agree in gender and number with the subject.

The subject here is (yo) and is being imagined as a single male speaker, so:

(Yo) no me siento tan preocupado.

If the speaker is female:

(Yo) no me siento tan preocupada.

If it’s we:

Mixed or all‑male: No nos sentimos tan preocupados.
All female: No nos sentimos tan preocupadas.

Why use he estudiado instead of estudié?

He estudiado is the present perfect (pretérito perfecto compuesto):
haber (he/has/ha…) + past participle.

In Spain, this tense is very commonly used for:

Actions recently completed, often in the same time frame as “today / this week, etc.”
Actions that have relevance to the present.

Here, realmente he estudiado presents studying as something done recently that still matters now (it influences how worried you feel right now).

You could say realmente estudié, but in Spain that sounds more like a finished, detached past (e.g. “back then I studied”), slightly less connected to your current state. In many parts of Latin America, estudié would be more normal in speech; but for Spanish from Spain, he estudiado is very natural.

What does realmente mean here, and where can it go in the sentence?

realmente here means “really / genuinely / truly”, adding emphasis:

porque realmente he estudiado ≈ because I really have studied.

Typical placements:

porque realmente he estudiado
porque he estudiado realmente (also OK, slightly different rhythm)
porque, realmente, he estudiado (with commas, more like “because, in fact, I have studied”).

Note: realmente does not mean “actually” in the sense of “in reality, contrary to what you might think” as strongly as English actually often does. For that nuance, Spanish more often uses en realidad:

En realidad, he estudiado bastante. – Actually / in fact, I’ve studied quite a lot.

Why is it porque (one word) and not por qué?

Spanish distinguishes four forms:

porque – “because” (answer, cause)
- No me preocupo porque he estudiado. – I’m not worried because I’ve studied.
por qué – “why” (question)
- ¿Por qué no te preocupas? – Why aren’t you worried?
porqué – a noun, “the reason” (less common)
- No entiendo el porqué. – I don’t understand the reason.
por que – rare combination of por + que from other structures.

In this sentence it introduces a reason (because I’ve studied), so it must be porque (one word, no accent):
…porque realmente he estudiado.

Can we say estoy no seguro or put no after the verb like in English?

No. In Spanish, the basic rule for negating a verb is:

no + verb (+ rest of sentence)

So it must be:

No estoy seguro… (correct)
Not:
Estoy no seguro… (wrong / unnatural)

Same with the other clause:

no me siento tan preocupado – I don’t feel so worried
- no comes before me siento, the conjugated verb (with its pronoun).

The negative no always goes directly before the conjugated verb (and before any attached clitic pronouns like me, te, lo, la, se when they precede the verb).