'you can not buy health, you must earn it'
Unfortunately there is a law in physiology that means, unless you apply stress to an organism (you), you won't improve your fitness. You certainly won't achieve your physical potential. And unfortunately creating stress can be hard work!
So you 'earning it', means hard work and unless you're used to physical hard work, which very few people are, its not easy. It can be mentally challenging to get out of your comfort zone and learn to work while you're uncomfortable.
The sessions I deliver to my clients take them out of their comfort zone and progress and they progress. Both in their physical work capacity and their mental resilience.
Where people start and end this journey are poles apart. But learning what you are truly capable of has a tremendous benefit both physically and mentally. For many people this can carry over and have a positive effect on other aspects of their life.
'Mental toughness is a measure of individual resilience and confidence that may predict success in sport, education and the workplace. ... Coaches and sport commentators freely use the term mental toughness to describe the mental state of athletes who persevere through difficult sport circumstances to succeed.'