That mental toughness and resilience can be trained. Get out and try hard things, find your limits, push those limits. People can adapt to the difficulties they face, we just don't face as many as people used to. When "normal" is enduring very difficult situations as a matter of course, you become accustomed and do not expect it to be easy. You learn how to deal with it. If you want to learn how to be tough like the days of old, go out and do tough things, seek those types of challenges.

People haven't changed much, our environment has changed.