Έχασα ένα κουμπί από το πουκάμισό μου, ακριβώς κάτω από τον γιακά.

Because Modern Greek often drops subject pronouns when the verb ending already makes the subject clear.

Έχασα already means I lost:

• έχασ- = the verb stem
• -α = I in this tense

So εγώ is not needed unless you want emphasis, contrast, or extra clarity:

• Εγώ έχασα ένα κουμπί... = I lost a button... (as opposed to someone else)

Έχασα is the aorist of χάνω and means I lost.

The aorist is the normal Greek tense for a completed event in the past. Here it presents the loss of the button as a single finished fact.

Compare:

• χάνω = I lose / I am losing
• έχασα = I lost

So this sentence is talking about something that happened, not an ongoing process.

Because κουμπί is a neuter singular noun, and here it is the direct object of the verb Έχασα.

So:

• ένα = a / one for a neuter singular noun
• κουμπί = button

Also, with many neuter nouns in Greek, the nominative and accusative forms are the same, so κουμπί stays κουμπί.

Because Greek is expressing the idea from/off my shirt, not just simple possession.

από here means from or off:

• Έχασα ένα κουμπί από το πουκάμισό μου = I lost a button from/off my shirt

This sounds natural when you mean that the button is missing as part of the shirt.

A genitive phrase such as ένα κουμπί του πουκαμίσου μου can also exist, but it sounds more like a button of my shirt or one of my shirt’s buttons. In this sentence, από is more natural because the idea is that the button came off / was lost from the shirt.

Because that is the normal Modern Greek way to say possession with weak possessive forms.

So:

• το πουκάμισό μου = my shirt
• literally, something like the shirt my

Common weak possessive words are:

• μου = my
• σου = your
• του / της = his / her

In everyday Greek, these usually come after the noun, not before it.

Because μου is an enclitic, a small unstressed word that leans on the word before it.

When an enclitic follows a word like πουκάμισο, Greek often adds an extra written accent to show the correct stress pattern of the whole phrase:

• πουκάμισο
• πουκάμισό μου

This is a normal spelling rule in Greek. It does not mean the word has changed meaning; it just shows how the stress works when μου is attached after it.

Because κάτω από is a fixed expression meaning under, below, or beneath.

So the sentence contains two different uses of από:

• από το πουκάμισό μου = from/off my shirt
• κάτω από τον γιακά = under/below the collar

Even though the same word appears twice, it is doing two different jobs.

Because γιακάς is a masculine noun, and after κάτω από Greek uses the accusative case.

So:

• dictionary form: ο γιακάς = the collar
• accusative: τον γιακά

That is why the sentence says κάτω από τον γιακά.

ακριβώς means exactly or right.

So:

• κάτω από τον γιακά = below the collar
• ακριβώς κάτω από τον γιακά = exactly / right below the collar

It makes the location more precise.

Yes, it is perfectly natural.

Greek word order is more flexible than English word order because Greek endings show grammatical relationships more clearly. Starting with the verb is very common.

So:

• Έχασα ένα κουμπί... = very natural
• Greek does not need to begin with I

The sentence flows as:

1. what happened: Έχασα
2. what was lost: ένα κουμπί
3. where from: από το πουκάμισό μου
4. exact location: ακριβώς κάτω από τον γιακά

The comma helps mark ακριβώς κάτω από τον γιακά as an added piece of location information.

With the comma, it sounds like:

• I lost a button from my shirt, right below the collar.

Without the comma, the sentence would still be understandable, but the pause and the explanatory feel would be weaker. So the comma is natural and helpful here.