The projects that do succeed have usually failed repeatedly, and many wrong approaches went into the final success. As you work through your career, you'll accumulate a lot of failures. But each represents a lot of work you did on various subtasks of the overall project. You'll find that a lot of the ideas you had, ways of thinking, even often bits of code you wrote, turn out to be just what's needed to solve a completely different problem several years later. This effect only becomes obvious after you've piled up quite a stack of failures, so take it on faith as you collect your first few that they will be useful later.
Research always takes much, much longer than it seems it ought to.
The rule of thumb is that any given subtask will take three times as long as you expect. Crucial to success is making your research part of your everyday life. Most breakthroughs occur while you are in the shower or riding the subway or windowshopping in Harvard Square. If you are thinking about your research in background mode all the time, ideas will just pop out. Successful AI people generally are less brilliant than they are persistent.