Topic: All relationships are based on convenience
At one time, I was slightly convinced that most relationships between people were based on convenience. Now I know it's absolutely true. I have seen friends become enemies and enemies become friends depending on the circumstances. Now I know this is true without question, as I have witnessed too many long-standing friendships (not involving me) terminate and become nasty because the circumstances made it costly.
Now I know people are so predictable and people management is so rational. Just pretend you are them and calculate their least risky and most profitable option, and you will usually be right. With that knowledge, you can build cooperative relationships that give you the most and take the least from you. Zomg, I can not believe I did not realize this sooner.