The old 25% rule (don't take a mortgage unless it is no more than 25% of your income) is ignored all the time. My mortgage was right at that, and I generally have never had trouble coming up with it. If I was doing 50-70% like some of my California friends I'd be as nervous as a rat at a cat farm. So I think you have to set some reasonable amount of technical debt as you say. Some issue simply dissolve, others get worse as far as the debt goes. Sometimes the business goes in a different direction and more dissolves. Other times maybe a big deal comes in for one of your products and you realize it might not be as easy to update for new needs (and $$ of income in particular) so you don't want to let it build up too much.