A first aid instructor once told me that if something is not urgent, it is recommended to not touch it unless you have something else to compare it. He said that if you see someone with a swollen wrist, it could be sprained or they could have a naturally thick and red wrist. As a result, unless that person has another wrist to compare it to, don't touch it.

Likewise, this can often be done with people and their attitudes. If a person trips on the street and someone else comes and helps them up, odds are they could be a nice person. He could also be a rapist who's an opportunistic killer. So unless you have some other base of his personality to compare it to (i.e. does he normally just help people and then walk away or does he often help people up and then stalk them), you can't really make a judgement.

Of course, that's a direct comparison, the corollary to this formula is seeing the norm, seeing the new case and then drawing the comparison and differences and then forming an idea over that. It's not an exact science but quite often, it is more accurate than the beliefs of the subject person themselves, simply because they're subject to their own bias. How often does a person really look at themselves and say "I will end up doing this even though it seems absolutely unlikely at the given time. This is because that is the outcome every time this has occurred."

Oh, and I see you Elena.