"Understand nature’s practical lessons."
Dalio’s main point here is similar to the one Joe Madden famously borrowed from The Marines: "Embrace the suck."
Things aren't good or bad. They just are. And greatness lies on the other side of things we call bad. Every hurdle is an opportunity to grow. Every failure is an opportunity to learn.
Dalio writes, " “Man needs difficulties. They are necessary for health.” Yet most people instinctively avoid pain."
What we need is eustress, or stress that is sufficient to create a positive adaptation. We need to push our bodies in the gym and challenge our minds with complex thoughts, deep conversations, and difficult books.
Unfortunately, many seek out comfort and look for happiness in the form of money and acclaim. But research has shown that once your income is sufficient for security, more money does not make you happier.
We should instead look for happiness through growth. We should challenge ourselves to get better by putting in the difficult work.
This comes straight from Maslow's Hierarchy Of Needs, which states that the ultimate goal of a lifetime is to reach a point of self-actualization. Be all that you can be. Become the best version of yourself. Find your ceiling.
It may sound trite, but it's true.