"I can't believe that he asked you for $20 and you just gave it to him.
He's a faker. Aren't you upset with yourself?"
"No. But he's really upset that he didn't ask for more!!"
"And you shall rejoice with all the good that Hashem gave you."
(Divorim 26:11) Rav Mordechai Gifter zt"l (and expounded by Rabbi Zelig
Pliskin) says that it is human nature to want more than we presently
have. Consequently, people aren't always happy when getting good things
because they think that it could have been even better. Therefore Hashem
commands us that we should rejoice 100% with the good that He gives us.