Well, depends on what kind of mood I am in, to be honest. Sometimes I'm just in a crappy mood and can't stand anybody. IRL I tend to be very willing to be understanding of strangers, or at least not assume the worst. If I know them and I can make a reasonable guess as to why they are doing what they are doing, that's another story. For example, if I overhear the person talking about doing well on a test, I would just assume that they're happy about doing well on a test and good for them. However, if I know the person is a complete braggart and uses their achievements to one-up other people, then I will think they're a stuck-up b***h.
I think it's some type of defense mechanism. If we assume the worst in people then we can think of ways to defend/attack if something bad happens. Granted that is incredibly silly but there are incredibly silly people out there.
It is more of a experience thing I assume. When a younger generation exists, this frame of mind does not. As a person grows older, they start to assume things based upon what they are raised to believe in; even if they don't agree with what they're were taught, unconsciously they do it because it is what they were raised in. We don't always remember most things we observe, but the unconscious mind records everything within range of what it can capture, even things we don't realize was there.
Honestly, we all do it don't we? If someones wearing a short skirt, we think 'wow she must be such a slut' even though maybe shes just grown out of it, or she has low self esteem and just wants to fit in.
And if someones talking about how they did really well on a test, or how they got into an accelerated class, once again we think ' wow they are so up theirselves, they must be a stuck up b***h' even though maybe they just finally had something to be proud of.
We all do it, and it happens to most of us at some point in our lives.
So feel free to discuss your experiences with this, your opinions, and if you agree or disagree with this .
The examples you mentioned are not "assuming the worst", those would be "forming a bad first impression". Yes, we all form first impressions, and to tell you the truth, mine turn out wrong half the time. They're based on the simplest, stupidest things but they're there and you probably won't change them until you actually get to know that person, that's when your first impression would be altered to better or worse. As long as you are aware that it's merely a first impression and that they might not be like that at all, then you'll do just fine.
Assuming the worst of others would be expecting them to do something bad to you, or letting you down. I think it's more of a defense mechanism: you just automatically assume that no one will remember your birthday so that if it's true, and they don't remember it well, you knew that already and won't feel too bad or hurt about it. If they do remember it then it's fine and makes you happy. It's always better to expect the worse but hope for the best.
I like you, its not often people are even willing to see better in people. I usually judge people on their honesty, I hate liars, cowards, or arrogance but other than that I pretty much try to find the best in people.
because most people have experiences in which they have been severely let down or disappointed by someone they thought they could trust, or have heard terrible stories of the aforementioned, which leads them to be cautious and prejudiced against others.