Humans are irrational. Even the person who thinks themselves the most rational will do irrational things from time to time, especially under stressful situations.
And if you think you can always overcome mental intertia and will yourself to do something: "Brain Scanner Can See Your Decisions Before You Make Them"
http://news.ycombinator.com/item?id=162863
And if you think you can always overcome mental intertia and will yourself to do something: "Brain Scanner Can See Your Decisions Before You Make Them" http://news.ycombinator.com/item?id=162863