As others have mentioned, the OP doesn't have "control" of a thread, and posters are therefore welcome to go off on tangents: So you could have a situation where the OP posted one question, but subsequent posters choose to answer other questions (questions not asked), essentially providing advice not solicited, etc. That hasn't typically happened in threads I've started, but it has happened once recently, in a medical-related thread. I posted a few "thanks for your opinions, but that wasn't really what I was asking" messages and then just ignored the replies that continued along that vein. Again, the OP cannot control that stuff.
I have seen, though, a lot of threads started by folks who really were just asking a question for which they only wanted one answer. That's very different than the scenario I outlined above, where the OP asks one question and posters answer other questions. By contrast, in this type of thread, the OP is not really looking for answers, but rather just looking for ratification, typically of a one-sided perspective that they either know, or at least suspect, is not universally endorsed. They want everyone to agree that what they want to do is what they should do or should be able to do, when the reality is probably quite different, i.e., where there are a lot of good reasons why the OP should do something else, or why the OP may not be able to do what they want to do. Many of those threads tend to get locked, eventually, it seems, when the OP doesn't get kind of ratification that they were looking for.