I don't think there's a balance of letting things go or standing up. For example, the course you asked for the refund may not have met your standards or expectations, in which case you can be justified in asking for a refund if they didn't do what they suggested they would on selling the course to you.

However, it's also about standing up for yourself/others productively. Such as when you demanded the refund did you just rant and rave or did you give justification as to why you believe a refund is due.

There are times, usually when the cost isn't worth the time or effort, to let things go. If someone makes joke about you then you don't always need to defend yourself if it's just a bit of fun. In fact, in that situation you'll show much more insecurity if you feel the need to defend yourself and ultimately the joke is harmless.