think about it if we treated every single situation as a completely new one it would take ages to do anything amd we wouldnt be able to priorities.
just think of situations if there are two tribes A and B, and u are in A. if one person from B attacks you one day and u escape. now the next time you see someone from tribe B (say they have certain face paint), u could treat this as a new situation, like u never had the previos incident. but it may be wiser to assume all peole from tribe B are hostile. of course the previos event could have been just chance, or u insulted him with ur body language. but untill something proves that this person n tribe B is not goin to attack you u should assume he very well might.
another more modern example. u are a begger, u see someone dressed in am expensive suit or someone dressed in cheapish jeans and a dirty t shirt. who do u approach. u would approach the man in the suit as u steriotype him as a rich person. it may not be the case but it saves time to assume it is.
the problem with steriotypes is when they are taken as a certainty and when u are unable to alter ur opinion of them when new information presents himself. like all blondes are dum or wateva. maybe a fair few of them are but u cant assume that.
