Do you ever post an answer to a question knowing full well that the OP will not take the advice?

No. I answer the question with the hope that the OP can get something useful from me, and that I can put my point across in an argument. I can be persistent but only for certain time. If I see that there’s no way that the OP will listen, and they are too narrow-minded to consider my point, I just leave.

Why? Because I know once they won’t listen, there’s no way I can ask them to listen. The whole topic will turn into an endless argument (or even worse, a flame war) and not the question about the OP’s problem anymore, and it won’t be good for anyone.

Beside, the OP may be a troll and just have nothing better to do. Feeding them is just tiring and what they want us to do is to feed them. No need to waste my time on a troll.

Yes, certain users appear to ask questions purely to gain a reaction, one which they are determined to feed on & argue with, can be fun though, winding the fuckers up.

For most things and most questions, I think it’s rare for people to immediately absorb advice and instantly apply it to their lives. As with real life conversations, I’m not sure we are aware of how a conversation affects us. I have had people ask me questions, only to years later find that those questions were the seed of what was to become a major shift in my outlook and life. I’ve also had arguments with people in which they dismissed my position as “crazy”. Yet, a year later, they hold that “crazy” position and have no idea where it came from.

I think we all give ourselves advice as well. “I should really…” statements might go on for years, until suddenly we actually follow that advice. But are we in any position to really know why our self-advice was suddenly compelling? It’s possible that conversations we had with others – even when we dismissed their arguments or advice – ended up affecting us in ways we’re unaware of.

I guess what I’m saying is that we’re largely driven by unconscious processes. And since these are unconscious and we’re not aware of them, I don’t think we’re really aware of why we do things. When we argue or hear people give advice, it’s more data that goes into feeding the mysterious unconscious processes that drive our conscious thought and behavior. A conversation here on Fluther in which someone gives me advice I deem to be asinine may be just the thing that makes the difference in the future, and may affect change in my mind and life in ways that I will ever know.

So, yes – I do post in threads where it seems that the OP will not take the advice. It may help the OP in ways s/he will never know, it may prove helpful to another observer of the thread, and it may be helpful to me to express my thoughts here and to get pushback.

Often the very nature of the question itself will tell you that you’re talking to “the wall”.

This is a Q&A site, so your answer will be viewed by more than the OPer. Even if their mind is closed, if I have some insight that seems to be helpful, I’ll post it hoping that someone else may be helped.

Sometimes a member can bring out an aspect that no one else had seen and change the dynamic of the question altogether.

All the time.