Because 9 times out of 10, when a novice asks "Why not do it this way?" the veteran can provide a good reason.

Why veterans must learn from novices:

Because 1 time out of 10, when a novice asks "Why not do it this way?" there *is* no good reason.

(disclaimer: this is a rule of thumb, and pair programming isn't about sitting a 12 year old behind John Carmack for six hours.)