You do not know what you are asking

James and John, the sons of Zebedee,
came to Jesus and said to him,

"Teacher, we want you to do for us whatever we ask of you." 
He replied, "What do you wish me to do for you?" 
They answered him, "Grant that in your glory
we may sit one at your right and the other at your left." 
Jesus said to them, "You do not know what you are asking. 
Can you drink the cup that I drink
or be baptized with the baptism with which I am baptized?" 
They said to him, "We can." 
Jesus said to them, "The cup that I drink, you will drink,
and with the baptism with which I am baptized, you will be baptized;
but to sit at my right or at my left is not mine to give
but is for those for whom it has been prepared." 
When the ten heard this, they became indignant at James and John. 
Jesus summoned them and said to them,
"You know that those who are recognized as rulers over the Gentiles
lord it over them,
and their great ones make their authority over them felt. 
But it shall not be so among you.
Rather, whoever wishes to be great among you will be your servant;
whoever wishes to be first among you will be the slave of all. 
For the Son of Man did not come to be served
but to serve and to give his life as a ransom for many."
(Mk 10:35-45)