Probably the most important thing to enjoying running throughout your life, or to being an excellent competitive runner (if that's your goal) is to have as few injuries as possible. Injuries are ridiculously common among runners. You might as well classify it as an extreme sport. Running injuries often take you out of the game for weeks or months. I have discovered a secret for remaining injury free that was hidden in plain sight from me. Don't be tough.
About a year ago, I was going for a very short run in my neighborhood. I was only running for maybe a mile or two and I wasn't pushing too hard. I started to feel a pain in my knee. I thought to myself that I'd better be cautious so I'll just finish this run and then take the next day off. Wrong answer. I couldn't get the pain to go away for quite some time. I can't tell you how many times I've told myself "I'll just finish this run." In my experience, backing off right away or even walking home if necessary can save you from being out for a week or more.
The moral of the story is to listen to your body. This is a fantastic opportunity to plug barefoot running, so I can't resist. Shoes do a fantastic job of blocking pain, but not such a fantastic job of preventing injury. That pain is our body trying to tell us what to do to remain injury free and when we wear shoes we don't get that communication. If I had to summarize what barefoot running is all about, that is it. Barefoot running enables you to hear what your feet are telling you.
If you don't want to run barefoot (and I assume that's most people), don't miss the message. You can still listen to your body when something hurts. Work on your discipline to slow down or stop when your body is telling you to. You'll gain a lot more miles by being injury free than you'll lose by cutting a few runs short.