Opportunity cost is important to consider, but it's not the same as cash out of pocket. And if you're going to include the opportunity cost of the house, then

Opportunity cost is important to consider, but it's not the same as cash out of pocket. And if you're going to include the opportunity cost of the house, then you also have to look at the cost of other options. Having a mortgage house costs money, and rent costs money. A paid-off house that you can maintain yourself may be the cheapest option - though that's not true for everyone all the time. There are unconventional options that are much cheaper (camper, RV, tent) but that's a whole different lifestyle.