3. There are trolls out there
Trolls are the only creatures David and the rest of the gnomes aren't fans of. (And if you've ever been on the internet, you know why.) Even if you take precautions, sometimes you have to deal with jerks -- but don't let their negativity make you a negative person as well. Avoid falling into their traps, and waste as little time with them as you possibly can.
David also taught us that revenge is a dish best served...never. David saves a baby troll from drowning. Sure, the trolls are his enemies and he could've walked away as retaliation, but that's an ugly way to live -- even uglier than a troll