Sometimes we understand something in one area, but fail to carry over the underlying logic into another domain. Many statisticians understand statistics, but still get tripped up by simple thought experiments. People will take an elevator to the gym to use the stairmaster.
While we understand the benefits of stress in medicine and health, we fail to carry it over to other parts of life. Small stresses on your income can be good for keeping you from accumulating silent risk or becoming cocky. Small fights in your relationship can help it become stronger, and avoid big fights.