It is evil to lie and cheat on someone.
Dave and Bill played the lotto together with an equal share and Dave has find out they've won $1000.
Dave wants to tell Bill what amount they won.
Dave tells Bill they won 1000 dollars and that Bill is going to get 500 dollars share.
Dave tells Bill they won 400 dollars and that Bill is going to get 200 dollars share.
Bill later finds out Dave was telling the truth and is happy to continue partnering with Dave.
Bill later finds out Dave was lying and is angry and sad that Dave lied and stole from him.