Learn Hardcore Portuguese (Portugal): Quando estou cansado, exagero e acho que o exame foi um desastre. - When I am tired, I exaggerate and think that the exam was a disaster.

Estou cansado = I am tired (right now / at this moment).
Sou cansado would sound like I am a tired person (by nature), which is unusual and a bit odd in most contexts.

Since tiredness is a temporary condition, estou cansado is the natural choice.

Why is there no eu before estou or exagero or acho?

In Portuguese, the subject pronoun (like eu) is often dropped because the verb ending already shows who the subject is.

estou = I am
exagero = I exaggerate
acho = I think

So Eu estou cansado, eu exagero e eu acho… is grammatically correct, but sounds heavy and unnatural in this kind of sentence. Native speakers prefer the shorter version unless they need to emphasize the subject.

Why is there a comma after Quando estou cansado?

Quando estou cansado is a dependent clause (a time clause) that comes before the main clause. In European Portuguese (and standard written Portuguese in general), you normally put a comma after such an initial clause:

Quando estou cansado, exagero e acho que o exame foi um desastre.

If the quando clause comes after the main clause, you usually do not use a comma:

Exagero e acho que o exame foi um desastre quando estou cansado.

Why is everything in the present tense (estou, exagero, acho) if we’re talking about a general habit?

The present tense in Portuguese (like in English) is often used for general truths, habits, and repeated behavior, not only for actions happening right now.

So:

Quando estou cansado, exagero…
= When I’m tired, I exaggerate… (in general, whenever this situation happens)

The sentence describes a typical pattern, not one specific occasion, so the present is exactly the right choice.

Could I say sou cansado if I want to mean I’m generally a low-energy person?

You could, but it would sound unusual and often a bit off. Portuguese speakers usually express that idea differently, for example:

Ando sempre cansado. – I’m always tired.
Costumo estar cansado. – I tend to be tired.
Sou preguiçoso. – I’m lazy. (if that’s the intended meaning)

Sou cansado is grammatically fine but rare; it may be used in very specific, poetic, or humorous contexts, not as a normal everyday description.

Why is it cansado and not cansada or something else?

Cansado is an adjective that must agree in gender and number with the subject.

If the speaker is a man: estou cansado
If the speaker is a woman: estou cansada
Group of men or mixed group: estamos cansados
Group of only women: estamos cansadas

The sentence you were given simply assumes a male speaker (or uses the masculine as a default form).

Why is it exagero and not exagerar?

Exagero is the 1st person singular, present tense of the verb exagerar:

(eu) exagero = I exaggerate

Exagerar is the infinitive, like to exaggerate in English. In a normal sentence with a subject doing an action, you need the conjugated form, not the infinitive:

✅ Eu exagero. – I exaggerate.
❌ Eu exagerar. – I to exaggerate. (incorrect)

What’s the difference between acho que and penso que here?

Both acho que and penso que can mean I think that, but:

acho que is more common and colloquial, often expressing a personal opinion or impression.
penso que can sound a bit more formal or reflective, like I think / I believe after some consideration.

In this everyday sentence, acho que o exame foi um desastre sounds more natural and spontaneous in European Portuguese.

Why is it acho que o exame foi um desastre and not acho o exame foi um desastre?

In Portuguese, after verbs of thinking, saying, believing, etc., you normally use que to introduce the clause:

acho que… – I think that…
digo que… – I say that…
acredito que… – I believe that…

So you need que before o exame foi um desastre because that whole part is what you think.

✅ Acho que o exame foi um desastre.
❌ Acho o exame foi um desastre. (incorrect)

Can que be dropped, like in English I think the exam was a disaster?

In English, that can often be dropped (I think (that) the exam was a disaster).

In Portuguese, que is usually not dropped in this kind of sentence, especially in European Portuguese. You might occasionally hear it omitted in fast, informal speech, but the standard, natural form is:

Acho que o exame foi um desastre.

Why is it foi and not era or é?

Foi is the pretérito perfeito (simple past) of ser, used for completed events in the past.

o exame foi um desastre = the exam was a disaster (a specific exam that is over)

Alternatives:

o exame era um desastre – would sound like you’re describing an ongoing situation in the past (e.g. talking about how the exam was in general over a period), which doesn’t quite fit a single exam.
o exame é um desastre – the exam is a disaster (present tense), would be used only if you’re talking about it as something that still exists right now (for example, an exam paper or test format that still exists and is generally terrible).

Since we’re talking about one exam that already happened, foi is the natural choice.

Why is it o exame and not um exame?

O exame (with o) refers to a specific exam that both speaker and listener know about:

o exame = the exam (that we’re talking about, e.g. yesterday’s exam)

Um exame would be an exam in general:

Quando estou cansado, exagero e acho que um exame foi um desastre.
This sounds strange, like some exam (randomly) was a disaster, without clear context.

Because you almost always have a specific exam in mind, o exame is appropriate.

If I’m talking about the future, should I say Quando estiver cansado instead of Quando estou cansado?

Both forms are possible, but they mean slightly different things:

Quando estou cansado, exagero…
General habit or pattern, valid anytime (including future).
= When I’m tired, I exaggerate.
Quando estiver cansado, vou exagerar…
Refers to a specific future situation (future subjunctive estiver).
= When I’m (specifically) tired (in that future situation), I will exaggerate.

In your sentence, which describes a general tendency, the present estou is exactly right.