Why didn't the Cessna 337 make it?

My instructor has over 100 hrs on the Skymaster, and he always said
that the problem with the Skymaster crashes were untrained piltos who
didn't take imemdiate actions when needed. He mentioned the
Synchrophaser gauge, that would show you which engine was doing the
work. IT either pointed forward or aft, so looking at it, you'd know
which engine is not working. He also mentioned that to keep the aft
engine cool he would run up the aft engine after running the front,
then shut it off, taxi with front engine on, and start the aft when
he is rady for take off before entering the runway. It's common
practice for many airlines, so it shoudln't be a problem for a
properly trained Skymaster pilot...