"Psychologizing" is when we go past arguing that a position is in fact wrong, and start considering what could have gone wrong in people's minds to make them believe something so wrong. Realistically, we can't entirely avoid psychologizing - sometimes cognitive biases are real and understanding how they potentially apply is important. Nonetheless, since psychologizing is potentially a pernicious and poisonous activity, Arbital's discussion norms say to explicitly tag or greenlink with "Psychologizing" each place where you speculate about the psychology of how people could possibly be so wrong. Again, psychologizing isn't necessarily wrong - sometimes people do make mistakes for systematic psychological reasons that are understandable - but it's dangerous, potentially degenerates extremely quickly, and deserves to be highlighted each and every time.
If you go off on an extended discourse about why somebody is mentally biased or thinking poorly, before you've argued on the object level that they are in fact mistaken about the subject matter, this is Bulverism. Bulverism is flatly not okay on Arbital. If you want to speculate about what goes wrong in the minds of people who believe in UFOs, then a good way of doing this on Arbital would be to first link a page arguing that there are in fact no UFOs, and say "I think this page establishes there are no UFOs; if you're not familiar with the arguments, read that first. Given that I think there are in fact no UFOs, I will now psychologize about why people would mistakenly believe in UFOs…"
If that clear label makes your page less snappy, persuasive, and fun to read, please consider that to be an intended effect of this rule. Psychologizing is fun and that's why we want to take steps against it coming to dominate discussions here.