El problema no se soluciona por sí solo.

Here se helps turn solucionar into a form meaning to get solved / to solve itself rather than to solve something.

• solucionar algo = to solve something
  
  • Solucionamos el problema. = We solve the problem.
• solucionarse = to get solved, to sort itself out

So:

• El problema no se soluciona... = The problem doesn’t get solved / doesn’t solve itself...

In this sentence, se does not mean that the problem is consciously doing an action. It gives the verb a more middle/passive-like sense: the problem is not resolving on its own.

Not in the most literal sense.

A true reflexive idea is something like:

• Juan se lava. = Juan washes himself.

But in:

• El problema se soluciona

the problem is not literally acting on itself the way a person might wash himself. This is better understood as a middle or pronominal use: the problem gets solved / resolves itself.

So for a learner, the safest way to think of it is:

• solucionar = to solve
• solucionarse = to get solved / to sort itself out

In Spanish, no normally goes directly before the conjugated verb phrase.

So:

• se soluciona = it gets solved
• no se soluciona = it does not get solved

You do not say:

• se no soluciona ❌

Because the clitic se stays attached to the verb phrase, and no comes before the whole thing.

Por sí solo means by itself, on its own, or without outside help.

It adds emphasis. The sentence is not just saying the problem isn’t solved; it is saying it won’t be solved automatically or without intervention.

Compare:

• El problema no se soluciona. = The problem doesn’t get solved.
• El problema no se soluciona por sí solo. = The problem doesn’t get solved by itself / on its own.

So por sí solo highlights the idea that someone has to do something about it.

Because sí here is the stressed pronoun meaning self after a preposition.

Compare:

• si = if
• sí = self / himself / herself / itself, depending on context after prepositions like de, en, por

So:

• por sí solo = by itself

The accent is important because it distinguishes this word from si meaning if.

Because solo agrees with el problema, which is masculine singular.

• el problema → masculine singular
• therefore solo → masculine singular

If the noun were feminine, you would change it:

• La situación no se soluciona por sí sola.

If it were plural:

• Los problemas no se solucionan por sí solos.

So solo changes to match the noun it refers to.

Because Spanish normally uses sí to refer back to the subject in expressions like this.

• por sí solo = by itself / on its own

Using él here would sound unnatural in this structure. Sí is the standard reflexive form after a preposition when the subject refers back to itself.

You may also hear:

• por sí mismo

That is also correct and means almost the same thing. In this sentence, por sí solo is very natural.

No, that sounds wrong in standard Spanish.

Without se, solucionar is normally transitive, so it needs something to be solved:

• Ella soluciona el problema. = She solves the problem.

But:

• El problema no soluciona... ❌

makes el problema sound like the thing doing the solving, which does not work here.

You need se:

• El problema no se soluciona por sí solo. ✅

Spanish often uses the present tense to express a general truth, a principle, or something that is true in the current situation.

So:

• El problema no se soluciona por sí solo.

can mean:

• The problem doesn’t solve itself.
• The problem won’t get solved on its own.
• Problems like this don’t get solved automatically.

Even though English might sometimes prefer won’t, Spanish often uses the present for this kind of general statement.

Yes. A very common alternative is:

• El problema no se resuelve por sí solo.

This is also completely natural.

Very roughly:

• resolver = to resolve / solve
• solucionar = to solve / fix

In many contexts they overlap. Resolver is extremely common with problema, so learners will hear both.

Yes, that is possible, and native speakers do say it.

However, por sí solo is a bit clearer and more emphatic. It strongly conveys on its own.

So:

• no se soluciona solo = doesn’t get solved by itself
• no se soluciona por sí solo = doesn’t get solved on its own

Both are natural, but por sí solo sounds slightly more explicit and polished.

Modern standard Spanish normally writes it as solo, without an accent.

In this sentence, solo is part of por sí solo, where it functions as an adjective agreeing with problema, so solo without an accent is correct.

You may see older spelling with sólo in some texts, but current standard usage generally prefers solo unless someone wants to mark a rare ambiguity.