Do you ever have conversations like this with friends or family?
That house you're buying, you'll need the windows replacing.
Yeah, well, down the line, when we can afford it, I guess.
Oh, but those ones are so dated! And inefficient. New windows will save you a fortune on bills.
Yes, but we don't have the money to do it.
But think of the money you could save!
... 
Also applies to things like - why you're not going on holiday, going abroad, don't want to have dinner at a Michelin starred restaurant, getting a new car...
What do you actually say to these people to make them understand?
I used to have a much higher disposable income than I do right now, but I still understood that other people didn't have the same cash to splash, or the same priorities. How is it possible to not grasp the concept of 'no, I don't have a spare 20k [or whatever]??'