People are self deceivers.
Obviously they know what they want in the first degree context. However the more layers of abstraction and distance from familiarity, this awareness breaks down and at some point is self contradicting even to the point of hypocrisy.
As an engineer, I'd say sometimes they do. Depends on the person. It should be well known to people here that you need to sit down and interview clients to understand what they do and then see what they really want when building software and collecting requirements.
I think it really depends on how deeply the person has thought about the need. Do they understand the problem domain? How far from the problem are they? Abstract understandings of want (e.g. "I want to be happy") are far less useful than more specific ones (e.g. "I want to make $30/hr to cover my living expenses comfortably").
Do you know what you want? I suppose, in abstract, people want an infinite amount of novel pleasure, doled out over eternity, tempered by an infinite amount of comparable but possibly also novel discomfort and waiting to provide context for said pleasure, eased by a condition where they forget their past experiences so that they may enjoy things they liked again as if it were the first time?
There is even a lot of scientific evidence that there is a suborgan in our brain for sense-making, for post hoc rationalization after making a decision.
So if you want to know what someone wants don't rely on this sense-making guy, rely on the actions this someone does.
This explains why we see people doing something but arguing the opposite: It is platonism and in my opinion causes a lot of suffering.
I think I'm just weak. Stronger personalities will grit and pick up flow again. I'm just too weak to enjoy the fruits.