Mark 11:20-23 (also Matt. 21:18-22)

As they were passing by in the morning, they saw the fig tree withered from the roots up.  21 Being reminded, Peter said to Him, “Rabbi, look, the fig tree which You cursed has withered.” 22 And Jesus answered saying to them, “Have faith in God.  23 “Truly I say to you, whoever says to this mountain, ‘Be taken up and cast into the sea,’ and does not doubt in his heart, but believes that what he says is going to happen, it will be granted him.

Just after Jesus’ triumphal entry into Jerusalem (Mk. 11:9-11), He went to Bethany to retire (since it was late in the day). Then early in the morning of the next day on their way back to Jerusalem, Jesus was hungry and saw a fig tree. But He discovered that it had no figs on it, only leaves. So, He cursed the tree so that it would die. Well, it wasn’t until the next morning that it was discovered by Peter that the entire tree had withered and died.

(In Matthew’s gospel it suggests that it happened all at once, even the withering of the tree. But I think the text in Mark is more accurate, or clearer as to what happened. The cursing of the tree and its death happened immediately when Jesus cursed it, but I think it wasn’t noticed until the next morning by Peter).

Peter was the one that noticed the withering of the tree and knew that it was caused by Jesus curse on it. Jesus then took the opportunity to give Peter a lesson of faith. Hence, Jesus was keenly aware that Peter needed this faith lesson, and Peter was eager to receive it—just as he did when he tried to walk on water (and he did for a while).