... They've already tried and failed (well, more than likely quit) at what you're aiming for.
If you succeed, they will no longer have an excuse for quitting; their lack of achievement will be on full display (in their own minds). These people need you to fail/quit so they don't have to face a cold, harsh reality: They could have done more or done better. Your success will make that loud and clear.
It's not that they're "hating" on you, or have some deep need to see you, and only you, do badly. The people hoping against your success are just lonely and afraid of having the face the coldest piece of information out there.
The Truth.