Μην χαλάς τη μέρα σου για ένα μικρό πρόβλημα.

Μην is the particle Greek uses for a negative command or prohibition: don’t ...

A very important point for learners is that Modern Greek normally does not use a true negative imperative form the way English does. Instead, it uses:

μη(ν) + verb

So:

• Μην χαλάς ... = Don’t ruin ...
• not Δεν χαλάς ..., because δεν negates statements, not commands.

Compare:

• Δεν χαλάς τη μέρα σου. = You are not ruining your day. / You don’t ruin your day.
• Μην χαλάς τη μέρα σου. = Don’t ruin your day.

Χαλάς is the 2nd person singular form of the verb χαλάω / χαλώ, meaning things like:

• to spoil
• to ruin
• to break

Here it is addressing one person informally, so it means:

• you ruin / you spoil
• but after Μην, it functions as don’t ruin

So the structure is essentially:

• Μην = don’t
• χαλάς = you ruin / spoil

Together: Μην χαλάς = Don’t ruin

In this sentence, χαλάω / χαλώ means to ruin or to spoil in an emotional or metaphorical sense.

So χαλάς τη μέρα σου means:

• you ruin your day
• you spoil your day

This verb is very common in Greek and can be used in several ways:

• Χάλασε το αυτοκίνητο. = The car broke down.
• Μου χάλασες τη διάθεση. = You ruined my mood.
• Μην χαλάς τη μέρα σου. = Don’t ruin your day.

So it can refer both to physical breakdown and spoiling a situation, mood, day, plan, etc.

This is about aspect, which is very important in Greek.

• Μην χαλάς uses the imperfective form.
• Μην χαλάσεις would use the perfective form.

Very roughly:

• Μην χαλάς ... = Don’t be ruining / don’t keep ruining / don’t ruin in a general, broad, or ongoing sense
• Μην χαλάσεις ... = Don’t ruin as a single complete act

In this sentence, Μην χαλάς τη μέρα σου για ένα μικρό πρόβλημα sounds like general advice:
Don’t let a small problem spoil your day.

So the imperfective fits well because the speaker is talking about a general attitude or behavior, not just one isolated action.

In Greek, short possessive pronouns like μου, σου, του, της, μας, σας, τους usually come after the noun, not before it.

So:

• η μέρα = the day
• η μέρα σου = your day

In this sentence, μέρα is the object of the verb, so it appears in the accusative:

• τη μέρα σου = your day

This is a very normal Greek pattern:

• το σπίτι μου = my house
• η φίλη σου = your friend
• τη ζωή του = his life

So Greek does not usually say the equivalent of your day with your before the noun the way English does.

Both are related to the same article: the feminine accusative singular article την.

In everyday Greek, the final -ν is often dropped before certain consonants, and μέρα begins with μ, so τη μέρα is very natural.

So:

• τη μέρα = common, natural
• την μέρα = also possible

You will often see both in writing, depending on style and spelling preference.

So this is not a different word or meaning—just a common variation in whether the final -ν is kept.

Μέρα is in the accusative singular here, because it is the direct object of χαλάς.

The person is ruining what?

• τη μέρα σου = your day

That makes it the object.

So:

• nominative: η μέρα = the day
• accusative: τη(ν) μέρα = the day as an object

This is why the article changes from η to τη(ν).

Here για is best understood as:

• because of
• over
• on account of

So:

• για ένα μικρό πρόβλημα = over a small problem / because of a small problem

This is one of those cases where translating για as plain for can sound a little unnatural in English if taken too literally.

A very natural English rendering is:

• Don’t ruin your day over a small problem.

So yes, για often means for, but in this sentence it has the sense of because of.

Because πρόβλημα is a neuter singular noun.

That means the article and adjective must match it:

• ένα = neuter singular a / one
• μικρό = neuter singular small
• πρόβλημα = problem

So:

• ένα μικρό πρόβλημα = a small problem

Also, after για, the noun is in the accusative, but for many neuter nouns the nominative and accusative forms are identical, so it looks the same.

Because in Greek, adjectives often come before the noun, just as in English.

So:

• ένα μικρό πρόβλημα = a small problem

This is the most neutral and common order.

Greek can sometimes place the adjective after the noun, depending on style or emphasis, but here the basic order is the natural one.

It is informal singular, because it uses:

• χαλάς = you singular, informal
• σου = your singular, informal

So the speaker is talking to one person in a familiar way.

If you wanted to say the same thing to:

• more than one person, or
• one person formally

you would usually say:

Μην χαλάτε τη μέρα σας για ένα μικρό πρόβλημα.

That means:

• Don’t ruin your day over a small problem.
  or, to several people,
• Don’t ruin your day over a small problem.

Yes, you may hear both μη and μην.

In modern usage:

• μην is extremely common
• μη also exists, especially before consonants

So forms like these can both occur:

• Μην χαλάς ...
• Μη χαλάς ...

In this sentence, Μην χαλάς sounds completely natural and standard.

A helpful breakdown is:

• Μην = don’t
• χαλάς = you ruin / spoil
• τη μέρα σου = your day
• για = over / because of
• ένα μικρό πρόβλημα = a small problem

So the whole sentence is literally something like:

Don’t ruin your day because of a small problem.

And a very natural English translation is:

Don’t ruin your day over a small problem.