Why are people so greedy and mean?

Seriously I've only met a few kind hearted people in my whole life! And by a few I mean like 5! Everyone else seems to only care about them self! To make it even worse this one time I found an iPhone and returned it to its owner! (I knew who it was because they texted the phone saying to call them and return it!) But yet when people found out I did that they were like "what?! Why didn't you keep it? You're stupid!" Only one person said that he respected me for doing that out if like 15 people! Like why can't people be kinder and donate some time or money to a good cause. Or return something that they know who it belongs to! I had my iPhone stolen once a long time ago and never got it back! But yet when I found that iPhone I was talking about earlier after my iPhone was stolen I still returned it! Also why do people give you mean looks sometimes when you just give them a simple smile or a hello? I mean c'mon people!

People are looking out for number uno when it's not ethical or practical.

Not everyone has the same ideals as you, we're all different. For example, some of us might be skeptical of donating to some causes and thinking that we might actually be donating for something completely different, actually, that's just plain cynical. Greedy? Mean? Ha. That's a part of being human. Nobody is 'nice'. Nobody does anything expecting nothing in return. Everybody gets something out of doing something 'nice'. Be it physical, mental, or emotional gain. Have you ever heard of "Charity not for the sake of others?" Karma. They would like the same thing to be done to them if they were in that situation. Nobody is obligated to help someone out. I sometimes do 'nice' things when i'm in a good mood. It's kind of like a side effect.

One can't feel only happiness, they must also feel sadness. Thus, one can't feel only kindness, they must also feel greediness.

From a non-biased point of view, i would say that people are greedy and mean, simply because they are. You could say the same about people being kind and forgiving. In regards to 'people giving you mean looks when you just give them a simple smile or hello', think about what they might have experienced before that happened. I say hello to people and they give me mean looks or punch me. Therefore, i no longer say hello. People are curious as to why i avoid socialising with them now. You asked simply why people are so greedy and mean, however, i shall share with you some insight. People are greedy and mean because they believe others are greedy and mean. If people are greedy and mean, then you should just be all the more kind and forgiving.

But…

… Isn't it mean to pass judgement on others saying they are greedy and mean?

If few people practice (kindness in this case), even fewer will know what to think

even if people are thinking for themselves, always, some kind of examples are needed

people will always copy what is known, not often think of ways that are different or better

People have good qualities too

HUMAN NATURE!