Кто угодно может ошибиться, если спешит.

Кто угодно means anyone at all, whoever, or absolutely anybody.

It is a very common Russian pattern:

• кто угодно = anyone at all
• что угодно = anything at all
• где угодно = anywhere
• когда угодно = anytime

Compared with кто-то, the meaning is different:

• кто-то = someone
• кто угодно = anyone / no matter who

So this sentence is not talking about one unknown person. It says that this can happen to absolutely any person.

Because кто is grammatically singular in Russian.

Even when кто угодно means anyone, the verb normally agrees with кто, so you get:

• кто угодно может
• если спешит

Both verbs are in the 3rd person singular.

This is normal in Russian. English often thinks of anyone as semantically broad, but Russian follows the grammar of кто, which is singular.

Yes. The кто part declines, while угодно stays the same.

Examples:

• nominative: кто угодно
• genitive/accusative: кого угодно
• dative: кому угодно
• instrumental: кем угодно
• prepositional: о ком угодно

So in this sentence, кто угодно is in the nominative because it is the subject.

Because ошибиться is perfective, and here it means to make a mistake as a single completed event.

The idea is:

• может ошибиться = can make a mistake
• может ошибаться = can be mistaken / can make mistakes repeatedly, depending on context

In this sentence, the speaker is talking about one possible mistake that may happen when someone is in a hurry, so ошибиться is the natural choice.

A simple way to think about it:

• ошибиться = to make a mistake once, to get something wrong
• ошибаться = to be mistaken, or to make mistakes in general / repeatedly

For example:

• Он ошибся = he made a mistake
• Он часто ошибается = he often makes mistakes
• Ты ошибаешься = you are mistaken

So in your sentence, the focus is on one mistake happening under a certain condition.

Here может expresses possibility.

So the sense is not:

• permission: is allowed to
• physical ability: is able to

It is more like:

• can
• may
• it is possible for someone to

So Кто угодно может ошибиться means that it is possible for any person to make a mistake.

Because Russian often omits a subject pronoun when it is already understood from context.

In this sentence, the person who спешит is the same person referred to by кто угодно. So Russian does not need to repeat он / она.

The structure is basically:

• Кто угодно может ошибиться, если спешит
• literally: Anyone can make a mistake if in a hurry

English usually wants an explicit subject, but Russian often leaves it out when it is obvious.

Russian often uses the present tense for general truths, habits, and typical conditions.

So если спешит here means something like:

• if they are in a hurry
• when someone is hurrying
• if a person rushes

It is not limited to one specific moment. It expresses a general condition: whenever a person is in a hurry, a mistake is possible.

Because если спешит is a subordinate clause, and Russian normally separates subordinate clauses with a comma.

So the sentence has:

• main clause: Кто угодно может ошибиться
• subordinate clause: если спешит

That is why the comma is required.

Yes, that is also natural.

But there is a slight nuance:

• кто угодно = anyone at all, absolutely anybody
• любой = any person, anyone
• каждый = everyone, each person

So:

• Кто угодно может ошибиться sounds like literally anybody can make a mistake
• Любой может ошибиться is also natural, but a little more neutral
• Каждый может ошибиться means everyone can make a mistake

In many contexts, all three are possible, but кто угодно gives a particularly strong no matter who feeling.