- Be surprised when the son you named "Blackwood" ends up being evil.
 - Heroes use swords; gentleman heroes use cane-swords.
 - Don't ask a brilliant deductive mind to rip your whole life open at first glance thinking it will be a fun experience.
 - Maybe dissecting the recently hanged prisoners' brain wasn't such a bad idea after all.
 - If a villain tells you "I wouldn't do that if I was you" always stop what you're doing and assault him with a backup plan.
 - If you have the power to devise extremely powerful attack strategies and then execute them to perfection, only use it against lowlifes and not bear-men or arch-villains.
 
More at 100thingsilearned.com...
Hat tip @awilkinson