Suicide may be a matter of honour, a means of escaping a fate worse than death or the consequences of sheer despair.
It can of course also be done out of sheer bloody-mindedness, just to avoid being killed by a hated enemy.
Also see Self-Sacrifice, as it is subtly different to Suicide.

The icon for this category is the "Kamikaze" worm from Team 17's "Worms" video game.