The professional baseball season is long and is a physical grind with a lot of banged up and bruised bodies. What he said is true and I have heard it from many players. These guys have to perform at the highest level despite really not being 100% physically. They have to endure and persist through the pain. They actually learn to embrace the grind instead of avoiding or hating it.
I think many of us believe and expect the journey to achieve goals should be comfortable or easy. In fact, I believe that the higher the goal such as running a marathon or succeeding in professional sports, the journey is very much uncomfortable. There is pain, fatigue, and sacrifice.
If it is losing weight, getting that promotion or getting that degree, it isn't easy and a lot of it can be uncomfortable..a grind. These people achieved through the knowledge they had to embrace the grind and embrace the journey.
Don't let the rain keep you from staying on your journey.