if you ask yourself "should i skip/cut short training today?" due to pain, the answer is automatically "yes". it's not a matter of wussing out, it's a simple matter of missing 1 or 2 training sessions due to pain, as opposed to missing a week or more of training due to a full blown injury.
this rule has served me well, & every injury i've sustained in the past year has been a direct result of breaking this rule
happy training,
jf
Respectfully, I'd like to disagree with this, to a certain extent. For me, it depends what type of pain we're talking about. If it's a general achiness, sore muscle-type thing, a good workout in class is often the best cure.
If you are injured, that's something different, and then it depends on whether it's an acute injury that will heal quickly or a chronic one that could take you out of your training for weeks or months.
Many injuries can be worked around, if you
listen to your body. If a drill looks likely to aggravate the injury, or if you start a drill and find that it is aggravating whatever localized pain you have, step out of the line for a few minutes (let your instructor know before class if you have physical issues, or you might get reprimanded unnecessarily). In some cases where it is impractical to actively train a martial art (eg. broken leg), even sitting on the side of the class can keep you involved and actively learning (listening to the lesson, observing the other students, etc).
I see nothing wrong with taking a few days off to allow an acute injury to heal; taking weeks or months off waiting for a chronic one can often lead to many other issues (mostly mental, guilt-related, etc) that can result in people stopping training altogether. Many people that do the "I'm sore, so I'll skip class tonight" can start getting on the path where they skip more and more often, and eventually we just wonder what happened to them and why they faded away.
For me, the key is learning turning off my ego (which continually tells me I'm Superman) and listening to what my body is telling me (like "Don't kick above your waist tonight or you'll pay for it when that hamstring that's been tight for a couple of weeks goes "twang"") I'm getting to an age now (coming up fast on 40) that if I waited to be 100% healthy and pain-free, I wouldn't be training at all.
On the other hand, if you feel like you're coming down with something (cold, flu, etc), please do us all a favor and skip class to get some rest. We don't need you sharing your oncoming illness with everyone else in the dojo...
