We've all been there -- cheerfully minding our own business in a battleground when along comes a warlock to ruin our day. Fear, dot, dot, dot, fear, shadowbolt, fear, shadowbolt... And you've died with nary a chance to defend yourself. You may be tempted to run to the most convenient forum and yell "nerf locks! nerf fear!"
Well, people of that persuasion, I point you towards Stylewalker's Nerf Warlocks FAQ, which covers all the bases on why fear isn't always an "iwin" button. Like how it's on diminishing returns (on a shared timer with seduce, even) and breaks on direct damage (and becomes more likely to break on dot damage with more spell damage gear). Does fear alone win fights for warlocks? I doubt it -- I've fought with plenty of horrible players for whom fear wasn't near enough to win a fight.