Jealousy. You never need to put a cover on a bucket full of crabs because anytime one crab tries to climb out the others will pull it back in. Sadly, people (even friends) often act in this same manner when someone they know is excelling in some way.
A student in my class looked over my shoulder and saw me run my script in the lab. I thought she was just going to ask if she could have a copy of it, but instead she angrily accused me of plagiarism. When I asked where I was supposedly plagiarizing from, she instead just accused me of cheating. She went up to our professor in class and demanded that I received no credit for the assignment. The grades in this class were not curved in any way, so my grade would have no impact on her's. Luckily, the professor just laughed at her and said "What? I'm supposed to give him an F for being smarter than you? Write your own damn script if it's that useful.".
Most people would fail define the meaning of the work 'job'. According to many a job is
a. Set of tasks that you need to execute 9 am to 5 pm.
b. Every other person can only do what you can do and can only execute the same tasks.
c. Any exception to a) and b) is evil.
d. People in c) are generally heretics, non-team players and are gaming the system. And in overall disrupting market for everybody else.
Do you know why this happens?
Its because when people of the same peer levels stay together, work together and spend a lot of time with each other. They begin to assume they all own the same money, live same lives, and have more or less than other.
Now suddenly when somebody discovers years later that one of them after going back home, used to silently work a big part of their night in garage building and selling stuff. And all that has made him relatively rich compared to him and everybody else, they feel cheated.
Its like a untold, silent agreement among people that none of them will do anything everybody else isn't doing. So that when somebody has a better chance of making it big, they generally have it from a source where all can benefit from. Else everybody remains where they are.