If you take a careful look during the last semis downturn, they rose very fast to extreme valuations when there was not a sign of an upturn. And when the upturn came they crashed just as they were making lots of money and the companies were still not predicting a downturn.
I remember all of that because I was envious not participating in the price surge because I wasn't seeing any signs of an upturn and I did not have any previous experience on how this shit works.
It is just not obvious to most people. I guess that is the way it is supposed to be. But then again, who knows how it is going to play out this time. I just think that history is a just a guide to make a guess.