Underestimation Technique #1: The classic "I've got this!" approach to project management. You know, the one where you're 95% sure everything will go smoothly, until it doesn't.
Subpage: "The Art of Procrastination"
Subpage: "The Delusion of Being Overprepared"
Subpage: "The Joy of Repeatedly Rebuilding from Scratch"
Next Technique: "Overextension: The Art of Taking On Too Much"