Saepe enim fit ut facies serena mentem anxiam celare non possit.

Because it is inside an ut clause after fit.

In Latin, fit ut ... is a very common expression meaning it happens that .... After this expression, Latin normally uses the subjunctive. So:

• fit = it happens
• ut ... possit = that ... can / is able to ...

So even though English says cannot, Latin uses the subjunctive here because of the construction, not because the meaning is especially doubtful or hypothetical.

Fit ut means it happens that or it comes about that.

So the sentence is structured like this:

• Saepe enim fit = For it often happens
• ut facies serena mentem anxiam celare non possit = that a calm face cannot hide an anxious mind

This is a standard Latin idiom. A learner might want to translate fit very literally as becomes or is made, but here that would be misleading. In this sentence, fit is best understood as happens.

Because in this sentence ut introduces a clause of result/occurrence, not purpose.

After expressions like fit ut, accidit ut, and evenit ut, Latin ut is usually translated as that:

• fit ut = it happens that
• accidit ut = it happens that
• evenit ut = it turns out that

So here ut does not mean in order that. It simply introduces the content of what happens.

The subject is facies serena.

So the core of the clause is:

• facies serena = a calm/serene face
• celare non possit = cannot hide

Put together:

• facies serena ... non possit = a calm face cannot ...
• mentem anxiam celare = hide an anxious mind

The subject of possit is also understood as the subject of the infinitive celare, because with possum Latin works much like English:

• can hide
• cannot hide

Because it depends on possit, from possum.

In Latin, possum works with a complementary infinitive, just like English can often goes with a bare verb:

• potest venire = he can come
• potest celare = he can hide
• non possit celare = cannot hide

So celare is not strange or incomplete; it is exactly what possit requires.

Because facies is the nominative singular, and it is the subject of the clause.

This can be confusing because facies is a fifth-declension noun, and its nominative singular ends in -es:

• nominative singular: facies = face
• accusative singular: faciem = face as a direct object

Here the face is doing the action of being unable to hide, so it must be in the nominative:

• facies serena = a serene face

If it were faciem serenam, that would make it an object instead.

Because it is the direct object of celare.

The verb celare means to hide and takes a direct object: you hide something.

So:

• mentem = accusative singular of mens
• anxiam = accusative singular feminine, agreeing with mentem

Together they mean:

• mentem anxiam = an anxious mind

Latin shows this relationship with case endings rather than fixed word order.

Yes, the order could be different. Latin word order is much freer than English word order because the endings show the grammatical relationships.

Here:

• facies serena = serene face
• mentem anxiam = anxious mind

The adjectives agree with their nouns in case, number, and gender, so the meaning is clear even if the order changes.

For example, Latin could also say:

• serena facies
• anxiam mentem

The chosen word order here is natural and balanced, but it is not the only possible order.

Enim usually means for, indeed, or you see.

It is a postpositive word, which means it normally comes second in its clause, not first. So Latin says:

• Saepe enim fit not
• Enim saepe fit

This is completely normal. A natural translation here is:

• For it often happens ... or
• Indeed, it often happens ...

Saepe means often, and it modifies fit.

So the sense is:

• it often happens that ...

It is not describing the face or the mind. It describes how frequently the whole situation occurs.

Yes, facies is feminine.

You can tell especially from the adjective serena, which is feminine nominative singular to agree with it:

• facies = feminine noun
• serena = feminine adjective

This agreement helps confirm that facies serena is one unit.

Because the subjunctive here is required by the fit ut construction, not because the meaning is might not be able to.

In other words, the clause is grammatically subjunctive, but in English the most natural translation is still straightforward:

• non possit = cannot

If you translated too mechanically, you might produce something awkward like may not be able to, but that would usually sound wrong in this sentence.

A helpful way to break it down is:

• Saepe enim fit = For it often happens
• ut = that
• facies serena = a calm face
• mentem anxiam = an anxious mind
• celare non possit = cannot hide

So the sentence has:

1. a main clause: Saepe enim fit
2. a subordinate ut clause with the subjunctive: ut ... non possit

This is a very useful pattern to recognize in Latin.