My spending habits changed considerably when I started to include the cost of real estate required in my calculations.

I encountered this first in a forum discussion about boilers - someone pointed out that the largest cost component isn't even the unit itself, but all the space it takes.

Anyway whenever I think of buying a treadmill, I remind myself that the actual cost is an additional €4500 just for the real estate and perhaps a gym membership would have been cheaper, but since I still haven't gotten one, perhaps it's less important to me than I think.