Saving or building, which is more sensible?

That's exactly how I see it too. If someone doesn't want to handle money, then they have to feel what consequences it has. Only under pressure from suffering will the personal shortcoming be worked on

But what if I want to go on vacation, for example? Leave my wife at home and say: "Well, next time you watch your money better!" ?xD

Just because it is not from the money of the joint account, from my point of view it is not more bearable for the partner. Gone is gone, regarding the money.

Oh yes, it is much more bearable. First of all, there is a consumption brake in the form of unavailable savings (mine, that is) built in. And precisely BECAUSE we do not consider money per se as OURS or each a piece as HIS, it does not bother me: MINE is not being touched. Why is this very simple system so hard to understand?

But what if I already want to go on vacation? Leave the wife at home and say: "Well, next time you watch your money better!"

It is a person with a full income (hardly lower than mine), full personal responsibility, and there is no activity like parenting that is performed without compensation. How we organize ourselves for such things is known in advance and agreed upon together.

So: Yes, that would be the right answer in this extreme case. I am consistent about that too. But since that is known, surprisingly there is always enough so that something like that doesn’t happen, oh wonder...

Lack of coordination just leads to home trainers costing 2.5k€ that aren't used.

???

"My money, I want it, so I'll buy it."

What am I supposed to "coordinate" there? I could try to talk some sense into them, but from experience that's ineffective. If it fits in the room and I don't have a very good argument for why I need the space for something else, what am I supposed to do?

"Figure out how to get the heavy junk up to the upper floor yourself" is the only sensible contribution.
A year later, it was sold to a buyer who picked it up themselves.

Anyway, an irony: Everyone demands independent, free, self-responsible people as partners, but when they mean to manage their own fully earned money independently, discussions about agreements and joint accounts arise. Wash my fur, but don't get me wet...

Irony anyway: Everyone demands independent, free, self-responsible people as partners, but when they want to manage their own fully self-earned money independently, discussions about agreements and joint accounts arise. Wash my fur, but don't get me wet...

Simple example among many possible ones: You certainly agree on what you want to eat in the evening or on the weekend and not everyone cooks their own meal...