Meaning of Fatal mistakes:

 Meaning of Fatal mistakes: 

Fatal mistake: collocation pattern: adjective + noun

Meaning of Fatal mistakes: 

a bad mistake that has terrible consequences

For example

She is not wake up at early morning anyway. That is her a fatal mistakes for her life.

Every time, over thinking is a fatal mistakes

Cheating in an exam can be a fatal mistake.

I made a fatal mistake when I invested all my money in share market

Note:

A similar collocation is "fatal error"