Charles Spurgeon Commentary Mark 10:36-39

"And he said unto them, What would ye that I should do for you? And they said unto him, Grant unto us that we may sit, one on thy right hand, and one on [thy] left hand, in thy glory. But Jesus said unto them, Ye know not what ye ask. Are ye able to drink the cup that I drink? or to be baptized with the baptism that I am baptized with? And they said unto him, We are able. And Jesus said unto them, The cup that I drink ye shall drink; and with the baptism that I am baptized withal shall ye be baptized:" — Mark 10:36-39 (ASV)

And he said unto them, What would ye that I should do for you? They said unto him, Grant unto us that we may sit, one on thy right hand, and the other on thy left hand, in thy glory. But Jesus said unto them, Ye know not what ye ask: can ye drink of the cup that I drink of? and be baptized with the baptism that I am baptized with? And they said unto him, We can.

Again, he might have said, "You know not what you say."