“I can't believe I fell for that.”

You lost $4000 because you were scammed by a fake book publishing company. You are really angry at yourself for getting tricked by it. You say to a friend:

I can't believe I fell for that.

I can't believe I (did something)

People say this when they regret doing something:

I can't believe I used to go out with that asshole!

I can't believe I forgot to lock the door!

This is useful for talking about mistakes or bad decisions that you made.

fall for (a lie)

When someone lies to you or tricks you, and you believe them, you have "fallen for" their lie. So "falling for a scam" means that you were tricked by someone and they took your money.

You use "fall for ___" like this:

A: She said that she had lost her purse and just needed some money to get a taxi ride home.

B: And you fell for that?

I'm not falling for your lies any more!