"Breakthroughs" are not really how synthetic intelligence has progressed so far. Look at speech recognition, for example. So far, that has mostly been a long, gradual slog. Maybe we are doing it wrong - and there is an easier way. However, that's not an isolated example - and if there are easier ways, we don't seem to be very good at finding them.
Of course, "breakthroughs" is a cumulative impression: now you don't know how to solve the problem or even how to state it, and 10 years later you do.
Eliezer Yudkowsky and Scott Aaronson - Percontations: Artificial Intelligence and Quantum Mechanics
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