I am proficient, smart and capable.

Capability shows best in situations nobody trained you for. The boiler that failed on a Sunday. The form in a language you don't read. The cot assembled at midnight from instructions drawn by someone who had plainly never seen a cot.

Certificates only cover the narrow version, proof that you did what you were taught. The broader question is your response to an unfamiliar problem: whether you go quiet and work it out. You have done that more times than you've counted, mostly on days you'd have described as ordinary.