Why are people/friends so fickle?

There have been people in my life that have left an imprint. That means I cant forget them even though i want to. They have all moved on and im here wondering....what's the big idea! When people don't know me, they tend to have their own impression of me. Some put me on a pedestal while others look down on me. Each and every time I unknowingly prove that their idea of me is wrong. I think the people who put me on a pedestal, get disappointed when I don't prove to them how amazing I am. And the people who looked down on me, get disappointed when I don't prove my weaknesses. It seems that if I don't show a reason for someone to stick around, they will leave. I get so frustrated when people initiate a friendship and it seems to be doing okay, then one day they stop talking/texting/spending time with you. It would have been helpful if someone came out and told me why they suddenly feel they need to end the friendship. There is no prior warning, no non-verbal cues, and definitely no hard feelings. So why do people think its okay to just leave high and dry, and with tons of confusion?