Quando scrivo in fretta, può capitare che dimentichi l’apostrofo o chiuda male la parentesi.

Because Italian normally leaves out subject pronouns when the verb ending already makes the subject clear.

• scrivo = I write
• so Quando scrivo already means When I write

You could say Quando io scrivo, but that would usually add emphasis or contrast, not just state the idea neutrally.

Italian often uses the present tense for habitual or repeated actions, just like English does in sentences such as When I write in a hurry...

So Quando scrivo in fretta means something like whenever I write quickly / when I’m writing in a hurry as a general pattern, not just one specific moment.

In fretta is a very common fixed expression meaning quickly / in a hurry.

A few useful points:

• fretta is a noun
• after in, Italian often uses noun phrases adverbially
• so instead of a simple adverb, Italian often says in fretta

It works a lot like:

• in ritardo = late
• in silenzio = silently / in silence

Both are possible, but they are slightly different in tone.

• capita che... = it happens that...
• può capitare che... = it can happen that...

Using può makes the statement a bit softer and more about possibility. It suggests that this is something that may happen from time to time, not something that definitely or regularly happens.

Because che introduces a subordinate clause: the thing that may happen.

So the structure is:

• può capitare = it can happen
• che dimentichi l’apostrofo o chiuda male la parentesi = that I forget the apostrophe or close the parenthesis badly

This is a very common Italian pattern:

• Può succedere che...
• Può darsi che...
• Capita che...

Because after expressions like può capitare che, Italian normally uses the subjunctive.

The idea is not presented as a simple fact, but as something possible or occasional. That is why you get:

• dimentichi instead of dimentico
• chiuda instead of chiudo

This is a very common rule with impersonal expressions of possibility, uncertainty, or evaluation.

Because both verbs belong to the same clause introduced by che.

So this part:

• che dimentichi l’apostrofo o chiuda male la parentesi

means:

• that I forget the apostrophe or close the parenthesis badly

Once che introduces the subjunctive clause, both coordinated verbs stay in that same mood.

Because the article changes depending on the noun that follows.

• apostrofo begins with a vowel, so the singular definite article becomes l’
• parentesi begins with a consonant, so it keeps la

So:

• l’apostrofo
• la parentesi

A nice detail here is that apostrofo is masculine, but before a vowel the article is still just l’.

Italian uses definite articles more often than English does, especially with nouns used in a general or typical sense.

Here the speaker is referring to the punctuation marks as the specific things one may forget or misuse while writing. So using the article sounds natural:

• dimenticare l’apostrofo
• chiudere male la parentesi

This does not necessarily mean one particular apostrophe or one particular parenthesis in a very literal sense; it is just standard Italian usage.

Male is an adverb meaning badly / incorrectly. It modifies the verb chiuda.

So:

• chiudere male la parentesi = to close the parenthesis badly / incorrectly

In context, it suggests making a punctuation mistake, such as not closing it properly or placing it wrong.

Yes, here it is singular.

Parentesi is one of those Italian nouns whose singular and plural have the same form:

• la parentesi = the parenthesis
• le parentesi = the parentheses

So the article tells you whether it is singular or plural.

Yes. That would also be natural.

For example:

• può capitare di dimenticare di mettere l’apostrofo
• può capitare che dimentichi l’apostrofo

The version in your sentence is especially useful because it coordinates two finite verbs neatly:

• dimentichi
• chiuda

So the structure feels balanced and smooth.