Do not be discouraged when God is good to all His children. He does not have favorites.
Read: Genesis 4:5-7
but on Cain and his offering he did not look with favor. So Cain was very angry, and his face was downcast.
6 Then the Lord said to Cain, “Why are you angry? Why is your face downcast? 7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must rule over it.