text: why is it that when you meet someone for the first time you know if it's going to work out within minutes?   as idrathernotsay says, we form our most important impression of others in no time at all.  i'd only like to add that i believe you are mistaken when you think that we know "it's going to work out". we have formed an idea of a person and we treat them a certain way, expecting somthing or other. none of this means that we are right. our first impression of somebody can be completely wrong (and often is).