In this passage The Wart - who will become King Arthur - has learned that his childhood companion Kay will soon be knighted while he, because of his uncertain parentage, will not. Instead, he is to be Kay's squire. What upsets The Wart is not that he won't be Kay's equal, or that he won't get to joust and fight and do all those knightly things, but that Kay, in preparation for this new life, has distanced himself from Wart and left him all alone. Mourning this loss of childhood joy and companionship, he turns to his wise tutor, Merlyn
"The best thing for being sad," replied Merlyn, beginning to puff and blow, "is to learn something. That is the only thing that never fails. You may grow old and trembling in your anatomies, you may lie awake at night listening to the disorder of your veins, you may miss your only love, you may see the world about you devastated by evil lunatics, or know your honor trampled in the sewers of baser minds. There is only one thing for it then - to learn. Learn why the world wags and what wags it. That is the only thing which the mind can never exhaust, never alienate, never be threatened by, never fear or distrust, and never dream of regretting. Learning is the thing for you."
The Once and Future King