[After James' and John's mother asked Jesus for them to have places of power in the Kingdom,] Jesus answered by saying to them, "You don't know what you are asking! Are you able to drink from the bitter cup of suffering I am about to drink?"
"Oh yes," they replied, "we are able!"
Jesus told them, "You will indeed drink from my bitter cup. But I have no right to say who will sit on my right or my left. My Father has prepared those places for the ones he has chosen."
— Matthew 20:22-23 NLT
Jesus saw through the mother's inquiry into the ambition of her two sons. When confronted, very much like Peter's braggadocio in later episodes, they are full of confidence in themselves. They think they deserve this opportunity and reward. They think they can handle whatever comes.
Very much like little children who want more information than they can process and more experience than they can handle, these two are like younger siblings wondering why they can't have the same privileges as their much older brother or sister. While there may be a very good explanation for their mother's question, the answer is beyond their grasp to understand. The two sons had no clue what they were signing up to do, but some day later, they would.
Loving Father, forgive me when I have overestimated my strength. I don't want to assume too much, whether it comes from arrogance or ignorance. I long to be used by you for your glory, but I don't want to become puffed up over accomplishments for which you alone deserve the credit, glory, and praise. In Jesus' name, I pray. Amen.