The raid is falling apart. You're on a boss you've downed before, but now it seems impossible to make it out of phase 1 because people keep failing on mechanics they should already have mastered. Ranged DPSers are standing in fire. Healers aren't popping CDs when the boss smacks the tank with its hard-hitting ability. Melee DPSers aren't switching to the adds in time, so they wipe the raid. Tanks can't seem to position the boss correctly. The raid is falling apart.
So what is it that will motivate your group to pick up the pieces, stop failing, and win?
Some group or raid leaders seem to think anger is the best motivator. They get stern, raise their voices, and threaten to kick the next person who fails, hoping their severity will prod everyone to victory. Some take a sarcastic tone, mocking group members until they clean up their act. "Wow, what a pro-mage move -- you Blinked right into that explosion. You should really think about doing this for a living." Others seek to break the tension and frustration by giving everyone a short break. Perhaps a reminder of the rewards works best, since shiny new loot is a great incentive for most. Sometimes even humor does the trick; it's just a matter of getting people to LOL at how pathetic that last attempt was or how ridiculous their character looks while riding Magmaw.
Since people are different, though. Sometimes one method of motivation doesn't work for everyone in the group. The angry lecture approach can backfire when group members get so worried about failing that they freeze up and stand still instead of doing their jobs. Taking a break or laughing for a few minutes can have the unintended result of breaking the raiders' concentration, at which point their loss of focus causes even more fail.
So what is the best motivation for you to overcome obstacles, perform at the highest level, and succeed?