Why think in blacks and whites, yeses or noes, rights or wrongs? Because if you don't get the correct answer ("this is a tiger") immediately, the saber-toothed tiger may eat you. Evolutionarily speaking, the brain, or the reactive part of it, may be programmed to make life-or-death decisions instantaneously. Unfortunately it can make the wrong decisions instantaneously, too.

But if you miss identifying the tiger and it is a tiger, you die and your brain's tendencies do not get passed on to the next generation. If you think it is a tiger and it is not, your tendencies probably still do get passed on.

Unless, of course, the thing you thought was a tiger is a human instead.