What most young programmers need to learn
<i>> Code in comments [...] When asked applicants are usually well aware that commented-out-code is confusing, but somehow they almost always have it in their code.</i><p>To my experience this is a common symptom of not using a version control system. You change a line of code, but you want to be able to undo if it doesn't work, possiblay half an hour later when you changed other places of your code (so your editor's undo is of no use).<p>I also see this from people who are using VCS, but that's mostly because they are overcautious and/or have not really gotten "warm" with the VCS.<p>A final, very small percentage are familar with VCS and confident with their code, but leave that commented stuff in there accidentally. The usual cause it that they have not (yet) acquired the habit of reviewing the diff before committing.