A pattern I've seen in many different fields: even though many people have worked hard in the field, only a small fraction of the space of possibilities has been explored, because they've all worked on similar things.
Even the smartest, most imaginative people are surprisingly conservative when deciding what to work on. People who would never dream of being fashionable in any other way get sucked into working on fashionable problems.
Some of the best places of all to find new ideas are fields that people think are played out, because they've already been fully explored. Essays, Lisp, venture funding – you may notice a pattern here.
The best protection against getting drawn into working on the same things as everyone else may be to genuinely love what you're doing. Then you'll continue to work on it even if you make the same mistake as other people and think that it's too marginal to matter.
