Avery looks up to Derek and admires his smarts. Avery's always hated that he could never be as smart or even try to be. Because every time he tries, he fails.
Derek is aware of the self loathing Avery goes through and that's the reason he left the signs.
With the time he had left, he didn't get to properly talk to Avery and reassure him. He would have told him, that it doesn't matter how smart he is or how much he's failed. If he can solve a puzzle or cipher or tell if somethings following him. He just needs to believe in himself. He is a person no matter what.
-Derp anon :3
SFAWTDE 2 SPOILERS
Avery's self-loathing does seem to be a pretty significant part of his video, especially when being snapped out of it by a pair of signs simply saying "you matter."














