Gold nuggets the hands of the miner. The working hands of a peasant with pure gold. top viewgettyOne thing I’ve always been astonished by is how fast a winning strategy (in investing and in life!) can suddenly slam into a wall—and start causing a lot of pain.Consider, for example, the life of a mortgage banker in the 2000s: They made easy money for years, then the subprime-mortgage crisis threw them out of work overnight.This happens in investing, too, which is why it’s always good to stay humble and well-d ...