Popa
Aing davar omeid is a Gemara. I don’t have the source but it’s a well know Gemara
It is not a gemara, it is a well known made up narishkeit. It was invented by bad parents and teachers to explain why they were unable to motivate kids properly.
And it is apikorsus too. Since sometimes you will want to do something good and Hashem will not let you for whatever reason He has. Like Moshe entering eretz yisroel.