This is (not "this's") the sixth thread you have started with the same unsatisfactory title.
A better title would have been 'If I've done it by mistake...'
Extract from the Posting Guidelines:
'Thread titles should include all or part of the word/phrase being discussed.'
I have noticed your tendency to use non-standard contractions — such as this's for this is — and standard contractions incorrectly — such as Yes, I've as a complete sentence instead of Yes, I have.
RegardingI don't know what it means."If I've done it by mistake, this's not my fault because he wasn't listening me when I was asking"
Student or Learner