A guy is repeatedly told by his parent's he's a failure and will never ammount to anything because he's stupid.
Annoyed, but determined, he leaves home and sets about his life, promising his family that despite their lack of faith he will make it, and be there for them when they need him.
In a little while through hard work he has set up his own business which is thriving. Years later he has become a millionaire. Every month in the post he sends his parents a cheque in the post for several thousand pouds, to thank them for raising him.
Every month his parents fail to cash the cheque due to a deliberate spelling error on it, to thank them for their belief.