The people you spend the most time with affect how you think and what you do.
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People are incredibly hard to change.
Spent half a year teaching someone programming. They told me they wanted to learn, etc. Ended up doing most of the bootcamp work for them so I could explain it to them, etc. This person had 5 day breaks where they didn't study a single thing. This also goes with "look at what people do, not what they say, or how they present themselves."
That also comes down to "don't waste time on shitty people." I used to spend time with everyone because of naivety, then I realized just how precious that time is and a lot of people just waste it.
In one interpretation, that's a scary thought encouraging selfishness. In my view, it's a pragmatic description of reality, encouraging judiciousness. I still find great joy in helping others, sometimes at some expense to myself, but I now feel a lot less bad about making value judgements before deciding if such a thing is worthwhile, rather than feeling obligated to help everyone that might want it.
Unfortunately, sometimes I find myself surrounded by people who have vastly differing life philosophies than my own (relatives, friends, spouse). In that case, the disagreement in a way pushes me harder to achieve what I want to out of sheer stubbornness than if I actually was surrounded by people who thought the same way as me.