how do you tell whether you want the thing or just the idea of it

I have not done anything and I am trying to work out whether I should.

The fantasy has been there a long time. Reliably there, since my twenties. It has never done any harm because it has never left my head.

What I keep circling is that I have no way of knowing whether I want the actual thing. Everything I have wanted this strongly in imagination and then done in life has been a disappointment at best. A house in the country. A particular job. The idea of both was better than the having.

There is a reasonable chance this is the same category and the honest description is that I enjoy thinking about it, and that if it happened I would be standing in a kitchen at ten at night feeling flat and slightly foolish and unable to take it back.

The stakes are the problem. If I try a restaurant I did not fancy, that is an evening. If I try this and it turns out I only liked the idea, then my wife has done something she cannot undo, at my request, for no reason.

I have read the accounts here from people who did it and found it was not what they wanted. What I cannot find is anybody who worked it out beforehand.

So is there a smaller version? A halfway house that tells you something real without committing anybody to anything? Or is the honest answer that this is one of those things you cannot know until you have already done it, in which case I would rather be told that plainly.