Your first line says "message", but the rest of your post talks about nodes. Which did you really mean?

If the answer is "node", as the other respondents have assumed, here's my opinion.

This is an age-old conundrum. The only really good advice is, Don't post until you're absolutely sure you want the entire world, including your grandchildren, to read it. Therefore, sleep on it, and preview, preview, preview. In many systems (USENET, for example), there is absolutely no possibility of recall or correction. In others (such as wikis) there is an enormous degree of post hoc editability, giving rise to a phenomenon known as wiki mind wipe, with a consequent echo of policies and mechanisms to combat it. Fortunately, PerlMonks is a little different from most other systems.

If you post, and it really is only an ohnosecond between the time you post and the time you regret, then yes, just edit the node to replace its contents with something like "sorry, mis-posted. please reap." The quicker you can do it, the smaller the window in which someone might have read the original content. The real deal-killer is if someone has replied to your node. Once that happens, edits to nodes should be limited to "Update"s, generally. And of course there's always the risk that someone has begun the process of replying to your node with its original contents, and not finally submitted their reply until after you make your change. If this happens, there is a great likelihood that the janitors will undo your edit.

That having been said... There is a FAQ on this issue: How do I change/delete my post? I assume you read it before posting your question. Oh, you didn't?

Somewhat relevant old discussion: Re^5: Unwritten rules variably applied. (lines)

Update: ysth kindly reminded me that it is possible to try kill a message on USENET, using a "cancel" message. Even so, it is rarely done, and very few USENETters indeed even know about it, let alone how to do it.