When there's smoke coming from my car's engine, or a weird noise, I take it to a mechanic, describe the symptoms and ask him to diagnose the problem and implement the solution.
When I order a new surfboard from my shaper, we'll discuss the sort of waves I want to be riding, what sort of surfing I'd like to be doing and my relative level of skill (low).
There are variables in both these situations: my own knowledge regarding the situation and my understanding of what is the best result for me, my level of trust with the person and the familiarity the person on the other end of the discussion has of my unique needs.
So when my knowledge is zero, and there's no room for subjectivity, the mechanic situation is the one. It doesn't matter what I know or what the mechanic thinks I want. The problem needs to be fixed. Easy. When there's a relationship between me and the other person, and history, and room for discussion, you get the surfboard scenario. Conversation ensues, ideas are shared, suggestions made and hopefully the service provider is strong enough to push back against what I think is best for me, and I trust them enough to accept their advice.
If you don't know which situation you're in, and treat it as one when it should be the other, chances are you aren't getting the results you should be. Next time you're in a restaurant you've never been to, have a look at the menu, pick something you think you want, and then instead of ordering it, tell the waiter what you feel like, and if it sounds like they know their stuff, order what they suggest. You might not get what you thought you wanted, but you could end up getting exactly what you needed.