Mistake is largely a result of intense fear (5)
I believe the answer is:
error
'mistake' is the definition.
(I know that mistake can be written as error)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for error that I've seen before include "1 down" , "Blunder or mistake" , "Trial and ___" , "Miscalculation" , "Faulty judgement" .)