A tale, maybe salutary.
In the early 1970s I was in my early 20s, married with mortgage, commuting quite long distance because I couldn't afford a house any nearer to London. My disposable income was very limited, and I had no savings. Every Friday lunchtime I went out for drinks with two colleagues, and one would always be last to buy a round, and then always halves despite the fact he had been bought a pint. He was single, lived with his parents near to the office and was on the same salary as me and the other guy. On being challenged on this one day, his excuse was that he had less disposable income than the other two of us: on further challenge, he explained that he saved 90% of his salary each month, and therefore, in his perverse logic, this was not disposable income. That was the last occasion on which he joined us for drinks.