realizing the life

May be I'm so silly that I can't understand why people are very confident of
what they are doing/thinking, especially "sinners".
Confidence which actually has no existence !!!

I know that there is no solid proof of god/fairness, but is there any proof of
no god ??
As far as my silly mind works, I don't've any such proof or listened to it ever.

Then why are sinners so much confident that there is
no god/rebirth/fairness/justice etc and will not get punished for their sins.
Is this not "hitting axe on our own feet" ??