Learn Hardcore Spanish (Latin America): A veces sentimos que cierta injusticia arruina nuestra felicidad. - Sometimes we feel that a certain injustice ruins our happiness.

A veces = sometimes
It usually goes at the beginning or somewhere before the main verb:
- A veces sentimos…
- A veces salgo temprano. = Sometimes I leave early.

Other similar expressions:

Algunas veces – also sometimes, a bit more formal or emphatic.
De vez en cuando – from time to time / once in a while.
A menudo – often, not sometimes.

All of these are fine in Latin American Spanish, but a veces is the most straightforward equivalent of sometimes here.

Why is it sentimos and not nos sentimos? Are both correct?

Sentimos comes from sentir, which has two main patterns:

sentir + noun / clause = to feel, to sense, to think
- Sentimos que… = We feel that / We think that…
- Siento frío. = I feel cold.
sentirse + adjective / adverb / como = to feel (in a certain state)
- Nos sentimos tristes. = We feel sad.
- Me siento bien. = I feel good.

In your sentence:

Sentimos que cierta injusticia arruina nuestra felicidad.
Here sentimos means we have the impression that / we perceive that, so it is not reflexive. That’s why there is no nos.

If you said:

A veces nos sentimos tristes porque cierta injusticia arruina nuestra felicidad.
Then nos sentimos would be correct because it’s we feel (ourselves) sad.

What is the function of que in sentimos que cierta injusticia…? Can you leave it out like in English?

Here que is a conjunction meaning that, introducing a clause:

sentimos que cierta injusticia arruina nuestra felicidad
= we feel that a certain injustice ruins our happiness

In English, you can often drop that:
We feel (that) some injustice ruins our happiness.

In Spanish, you almost never drop que in this kind of sentence.
You need it to connect sentimos with the whole idea that follows.

So:

✅ Sentimos que cierta injusticia arruina nuestra felicidad.
❌ Sentimos cierta injusticia arruina nuestra felicidad. (sounds wrong in Spanish)

What nuance does cierta add before injusticia? Is it like a certain injustice or some injustice?

Placing cierta before the noun gives the idea of some or a certain, in a vague, non-specific way:

cierta injusticia ≈ some injustice / a certain injustice
(we’re not specifying exactly which injustice, just the idea that some sort of injustice is involved)

If you compare:

una injusticia – an injustice (more neutral)
cierta injusticia – a certain injustice / some injustice (vague, lightly emphasized)
alguna injusticia – some injustice (also vague, but a bit more common/neutral than cierta in many contexts)

Also, cierto/cierta changes meaning depending on its position:

cierta injusticia (before the noun) = some / a certain injustice
injusticia cierta (after the noun) = a sure / true injustice (this is unusual; you’d more likely hear una injusticia real / evidente / clara).

So in your sentence, cierta gives a slightly literary or thoughtful tone: we’re talking about some kind of injustice that affects us.

Why is there no una in cierta injusticia? Why not una cierta injusticia?

In Spanish, cierto/cierta already functions like an indefinite determiner, similar to a certain. Because of that, you often don’t need una:

cierta injusticia = a certain injustice / some injustice

Using una cierta injusticia is possible, but it sounds more:

formal,
literary,
or emphatic, like: a particular, specific kind of injustice.

So:

cierta injusticia – completely natural and common.
una cierta injusticia – also correct, but sounds more marked or stylistic.

In everyday speech, especially in Latin America, most people would simply say cierta injusticia as in your sentence.

Why is arruina singular? Shouldn’t the verb agree with sentimos (“we feel”)?

Arruina and sentimos belong to two different clauses, each with its own subject:

A veces sentimos
- Subject: nosotros (implied “we”)
- Verb: sentimos (1st person plural)
que cierta injusticia arruina nuestra felicidad
- Subject: cierta injusticia (singular)
- Verb: arruina (3rd person singular)

So arruina is singular because it agrees with injusticia, which is singular.

If you changed the subject to plural:

A veces sentimos que ciertas injusticias arruinan nuestra felicidad.
Now the subject is ciertas injusticias (plural), so the verb becomes arruinan (plural).

Why is it arruina (indicative) and not arruine (subjunctive)? Doesn’t sentir que normally trigger the subjunctive?

This is a subtle but important point.

Sentir has two meanings that affect the mood:

Sentir que + indicative = to feel / think / sense that (opinion or perception)
- Sentimos que cierta injusticia arruina nuestra felicidad.
  = We feel / think that some injustice ruins our happiness.
- Here sentimos expresses a belief or perception, so Spanish uses the indicative (arruina).
Sentir que + subjunctive = to be sorry / regret that (emotion about something)
- Siento que eso te arruine la felicidad.
  = I’m sorry that that ruins your happiness.
- Here siento expresses regret, so Spanish uses the subjunctive (arruine).

In your sentence, the idea is more like “Sometimes we feel/think that some injustice ruins our happiness”, not “We are sorry that…”, so the indicative (arruina) is correct.

If you wanted the “I’m sorry that…” meaning, you’d need to change context and maybe the subject:

Sentimos que esa injusticia arruine tu felicidad.
= We’re sorry that that injustice ruins your happiness. (emotion → subjunctive)

How does nuestra agree with felicidad? Could it be nuestro felicidad?

Nuestra is the feminine singular form of nuestro (our).
Possessive adjectives must agree in gender and number with the noun they modify, not with the people who own it.

felicidad is feminine and singular: la felicidad
So you need: nuestra felicidad

Forms of nuestro:

nuestro – masculine singular (e.g. nuestro libro)
nuestra – feminine singular (e.g. nuestra casa, nuestra felicidad)
nuestros – masculine plural (e.g. nuestros amigos)
nuestras – feminine plural (e.g. nuestras ideas)

So:

❌ nuestro felicidad – wrong (gender mismatch)
✅ nuestra felicidad – correct

Why is felicidad singular? Why not nuestras felicidades like our happinesses?

In both languages, happiness / felicidad is normally treated as a general, uncountable concept:

nuestra felicidad = our happiness (as a whole, abstract idea).

In Spanish:

felicidad in singular = the general state of being happy.
felicidades (plural) usually means congratulations, as in:
- ¡Felicidades! = Congratulations!
- Te mando muchas felicidades. = I send you many congratulations / best wishes.

So nuestras felicidades would sound like our congratulations, not “our happinesses”.

For the meaning here, singular felicidad is the natural and correct choice:
nuestra felicidad = our happiness.

Can the word order change? For example: Sentimos a veces que cierta injusticia arruina nuestra felicidad or Sentimos que cierta injusticia a veces arruina nuestra felicidad?

Yes, Spanish allows some flexibility in word order, and your alternatives are grammatically correct, with small differences in emphasis:

A veces sentimos que cierta injusticia arruina nuestra felicidad.
- Neutral, very natural.
- Emphasis on A veces: Sometimes (not always), we feel this.
Sentimos a veces que cierta injusticia arruina nuestra felicidad.
- Also correct.
- Slightly more emphasis on the feeling itself; sounds a bit more formal or written, but still fine in speech.
Sentimos que cierta injusticia a veces arruina nuestra felicidad.
- Also correct.
- Here a veces is attached more directly to arruina:
  We feel that some injustice sometimes ruins our happiness (focusing on the frequency of the ruining rather than of the feeling).

All three are acceptable in Latin American Spanish. The original version (A veces sentimos que…) is the most straightforward and common.