I'll believe it when I see it spoken informal
Used to say that you think something won't happen.
Although she says she will finish her homework soon, I'll believe it when I see it.
A: Peter passed the driving test last year. B: Was he afraid of driving? I'll believe it when I see it.
To decide to believe someone‘s saying although they may not tell the truth
1. If you hang your hat on something, you depend or reply on it.
2. If you hang your hat on something, you believe or trust it.
If you take something as gospel, you definitely believe it without without any hesitation.
To express that you don't believe in something that someone has just said
People tend to like forbidden or illegal things just because they are forbidden or illegal.
He must have believed that stolen fruit is the sweetest, and he, therefore, cheated on his partner.