The general gist of any kind of physical training endeavor or any kind of pursuit in life is that you throw a stimulus at your body, i.e. you lift a weight or read from a book. And then your body will respond by adapting to that stimulus. You get a little stronger or you get a little smarter. That tends to be the general rule of how it works.
But it's far from optimal...
If you're serious about getting things done, making the gains, whatever they may be. If they are physical, academic, work or spiritual related. The how you approach this process is will ultimately determine the length of your journey from where you are now to your ideal destination and how much or how little time you spend pursuing something half heartedly.
Imagine you're out jogging or running because you are pursuing some sort of exercise related goal, whether thats because you want to lose weight or you want to qualify for the Boston Marathon. The end goal is irrelevant to what I am discussing here. You run for maybe a few minutes (Or maybe even for a few hours depending upon where you're at). And your legs start to hurt, you start to feel out of breath, you start to doubt that you will be able to hold this pace for much longer and that you need to ease up or maybe even stop. So maybe you should stop, right?
Right now in this moment of pain and hardship you have been gracefully presented with the opportunity to become better at whatever you're doing. Whether that is running, or learning about something new. This is where the effort and input on your end really counts. But don't get me wrong, I'm not suggesting we all go out, and run ourselves into the ground till our tendons snap and we pass out. Or read books for 24 hours solid, till out eyes bleed. Not at all.
"The hard part is knowing when your body genuinely needs rest as appose to when you're just being a pussy" Sebastian Kienle, Ironman World Champion 2014.
I am saying that when we are presented with that hardship, push yourself. The hardship is a GIFT. Its a wonderful opportunity for growth. Beyond that, you'll also be strengthening your mind, you'll build that habit of pushing yourself through difficult or uncomfortable situations. You'll be able to overcome more. You will be stronger. You'll have more energy to devote yourself to other things, the things and people most important to you.
Get out there and make it happen. When you think you can't carry on and you need to give up, keep going. Don't quit. Behind every pain and fear is a person you want to be.