There was a failure to recognize the deep problems in AI; for instance, those captured in Blocks World. The people building physical robots learned nothing.
Marvin MinskyWhat is intelligence, anyway It is only a word that people use to name those unknown processes with which our brains solve problems we call hard. But whenever you learn a skill yourself, you're less impressed or mystified when other people do the same. This is why the meaning of 'intelligence' seems so elusive: It describes not some definite thing but only the momentary horizon of our ignorance about how minds might work.
Marvin Minsky