Probably running in discomfort and knowing when to stop. I don’t really recall a time, in recent years at least, where I have run pain-free. It can grind you down a bit and it’s mentally tough to keep going when you’re uncomfortable. Again, I revert back to yoga, which has really helped my mental strength and focus. I don’t run comfortably, but I am able to work through the discomfort now by breathing, thinking about all the things I’m grateful for and reminding myself I’m privileged to be able to run and get out in nature.