The Four Chambered Organ

If you wear it on your sleeve, you're bound to get hurt.
If you wear it long enough it might grow some calluses.
No. It's a muscle.
You have to train it.
Expanding, general growth. You have to train it.
After every marathon you need to rest.
Wait for it to heal before continuing.
Every muscle needs to rest, even the complicated ones.
There's going to be aches. It's going to be sore.
Keep going.
If you train it long enough...
there won't be a guarantee of pain free days, no.
There will be less rest needed, less aches.
It's a muscle; it will be strong and be able to withstand more.
It will be better.