Which is correct "A for effort" or "E for effort"?

Question:and why? Here are two explainations I have hear:

A for Effort: as in ABCDF, poor contained by academics but tries sturdy therefore C+ contained by math but "A for effort".

E for Effort: as in ESU=Effort, Satisifactory, Unsatisfactory

This intermingle makes sense but where on earth did "E for effort come" from, mistake?
is there any epic behind famous tamil saying "siva poojayil karadi poondha maathiri"?Please explain if u know?

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is there any epic behind famous tamil saying "siva poojayil karadi poondha maathiri"?Please explain if u know?