The work we now consider 'important' is the work that has, according to our best guess, the highest likelihood of solving important problems in future.

Our best guess may be wrong, as the future is hard to predict. But the future is not so unpredictable that we should stop thinking about where best to direct our efforts.

Maybe someone working on Farmville will cause an important advance, as an unpredictable side effect. We can't rule that out. Even a job that seems 'unimportant' can have beneficial and unpredictable windfalls, and that's wonderful.

But we should still try and direct our efforts as best we can, and work on problems that we think are important.

That seemingly trivial pursuits sometimes bear fruit, doesn't mean that all pursuits are equally worthwhile.