A mi amigo le cuesta acordarse de la contraseña.

Yes, they both point to the same person, but Spanish often uses this double marking with indirect objects.

• le = the indirect object pronoun: to him / to her
• a mi amigo = a fuller phrase that clarifies who le refers to

So:

• Le cuesta... = It’s difficult for him...
• A mi amigo le cuesta... = As for my friend, it’s difficult for him...

In Spanish, this kind of indirect object doubling is very common, and often sounds more natural than leaving out le.

Here costar does not mean only to cost money. It also means to be difficult / to take effort.

The pattern is:

• A alguien le cuesta + infinitive

Examples:

• Me cuesta levantarme temprano. = Getting up early is hard for me.
• Le cuesta entenderlo. = It’s hard for him/her to understand it.

So in your sentence:

• A mi amigo = for my friend
• le cuesta = it is hard for him
• acordarse de la contraseña = to remember the password

Because the subject is the whole infinitive phrase:

• acordarse de la contraseña

An infinitive phrase is normally treated as a singular idea in Spanish.

So the structure is basically:

• [Acordarse de la contraseña] le cuesta a mi amigo.
• Remembering the password is difficult for my friend.

Since that whole action is singular, Spanish uses cuesta.

Because after costar, Spanish usually uses an infinitive to say what action is difficult.

Pattern:

• A alguien le cuesta + infinitive

So:

• Le cuesta acordarse...
• not Le cuesta acuerda...

You can think of it like:

• It is hard for him to remember...

After to in English, you use the base form; after costar in Spanish, you use the infinitive.

Because acordarse de is the usual structure meaning to remember.

• acordarse de algo = to remember something
• acordarse de alguien = to remember someone

So:

• acordarse de la contraseña = to remember the password

Without the reflexive pronoun and de, acordar usually means something else, such as to agree or to decide in certain contexts.

For learners, it’s best to remember acordarse de as a fixed expression.

Because se is part of the verb acordarse. It is not there to repeat mi amigo; it is there because the verb is pronominal.

The full dictionary form is:

• acordarse de

When the subject changes, the reflexive pronoun changes too:

• me acuerdo de
• te acuerdas de
• se acuerda de
• nos acordamos de
• os acordáis de
• se acuerdan de

In your sentence, the verb stays in the infinitive, so you see the dictionary form:

• acordarse de

Because acordarse requires de.

The pattern is:

• acordarse de + noun
• acordarse de + infinitive / clause

Examples:

• Me acuerdo de tu nombre.
• Se acuerda de llamar.
• Nos acordamos de que venías hoy.

So la contraseña is introduced by de because that is the preposition the verb needs.

Yes. Both can mean to remember the password.

• recordar algo
• acordarse de algo

So these are both possible:

• A mi amigo le cuesta acordarse de la contraseña.
• A mi amigo le cuesta recordar la contraseña.

For many learners, recordar feels simpler because it does not need se or de.

Still, acordarse de is extremely common in everyday Spanish, so it is important to know it well.

No. A mi amigo is the indirect object.

The subject is the action:

• acordarse de la contraseña

A good way to see it is to rearrange the sentence:

• Acordarse de la contraseña le cuesta a mi amigo.

Now it is clearer that remembering the password is what is difficult, and my friend is the person affected by that difficulty.

Yes:

• Le cuesta acordarse de la contraseña.

That means:

• It’s hard for him/her to remember the password.

But then we do not know exactly who le refers to unless context makes it clear.

Adding a mi amigo makes the reference explicit.

In standard Spanish, with this kind of structure, le is normally kept:

• A mi amigo le cuesta...

Leaving out le would sound unnatural to most speakers.

So even though a mi amigo is already present, Spanish still normally keeps the indirect object pronoun.

Yes. Spanish allows some flexibility.

These are possible:

• A mi amigo le cuesta acordarse de la contraseña.
• Le cuesta acordarse de la contraseña a mi amigo.
• Acordarse de la contraseña le cuesta a mi amigo.

The most neutral and natural version here is probably the original one.

Word order changes usually affect focus or emphasis, not the basic meaning.

Both are possible, but they are not exactly the same in feel.

• la contraseña = the password
• su contraseña = his/her password

Spanish often uses the definite article where English might prefer a possessive, especially when the owner is already clear from context.

Here, since we already know the person involved is mi amigo, la contraseña is perfectly natural. It is understood as the relevant password.

If you wanted to stress that it is specifically his password, you could say:

• A mi amigo le cuesta acordarse de su contraseña.

Not exactly. Here it is part of marking an indirect object, not a direct object.

Compare:

• Veo a mi amigo.
  Here a mi amigo is a direct object with the personal a.

• Le doy el libro a mi amigo.
  Here a mi amigo is an indirect object.

Your sentence works like the second type:

• A mi amigo le cuesta...

So this a introduces the person who is affected by the verb, not the thing directly acted on.

A very useful pattern is:

• A alguien le cuesta + infinitive

Meaning:

• Someone finds it difficult to do something

Examples:

• Me cuesta dormir.
• A Marta le cuesta concentrarse.
• Nos cuesta entender este tema.

And with your sentence’s structure:

• A mi amigo le cuesta acordarse de la contraseña.

This is a very common and natural Spanish way to talk about difficulty.