But how to decide whether a given datum is ‘bad’ or ‘good’ information before consuming said datum and linking it up with the rest of your memory? Maybe it looks utterly senseless at the time you first read it, but it might well be missing piece linking two large and so far separate areas together.
That applies to any decision; you rarely or never have complete information. The solution is to apply heuristics to make a preliminary judgment. For example, by coming to HN instead of any other source of articles you're implicitly deciding that being linked from here means there's a greater probability of the article being good (for any definition of good you prefer).