"We are able"

"James and John, the two sons of Zebedee, came up to Jesus, saying, "Teacher, we want You to do for us whatever we ask of You." ... "Are you able to drink the cup that I drink, or to be baptized with the baptism with which I am baptized?" They said to Him, "We are able." And Jesus said to them, "The cup that I drink you shall drink; and you shall be baptized with the baptism with which I am baptized."

James was the first to be martyred. John died last of all, of a natural death. So the "cup" wasn't martyrdom as we think of it, though that's the hymn suggests . I wonder which of the two had the harder row to hoe.