an idiom

[English4everyone]

I need an idiom to describe the person or the following situation.
When you compliment someone on being very good at doing things, you think everything is ok with him / her. You are so sure that you never think he / she will fail. But after a lot of praise and compliment, he / she fails.
Is there an idiom about this?

[Barb_D]

He or she has feet of clay.

What does it Mean to Have "Feet of Clay"?

[English4everyone]

Thank you very much. A nice idiom.
But please if there is something else that is close to this context, let me know.

[Rover_KE]

You could consider 'He flatters to deceive'.

There must be others; I'll keep thinking.

Rover

[BobK]

I've read 'Homer nodded' [Homer being famously wise/omniscient and 'nodding' meaning he drifted off/went to sleep], but I've never used it or heard it used.

b

[emsr2d2]

I need an idiom to describe the person or the following situation.
When you compliment someone on being very good at doing things, you think everything is ok with him / her. You are so sure that you never think he / she will fail. But after a lot of praise and compliment, he / she fails.
Is there an idiom about this?

I'm not quite clear on the situation. Are you talking about someone in whom you have implicit faith, someone who you assume will always succeed and you regularly tell him/her so, and yet inexplicably he/she suddenly fails at something? Or does this person regularly fail at things, but only after being given a lot of praise and compliments?