So everyone should use only his or her discretionary income to accumulate Bitcoin the only time you may go beyond that is when you have a strong backup funds.
Even with your explanation to @Solosanz, using the hypothetical $2k monthly earning that left out $500 as discretionary income, I'm of the opinion that it's still not a good thing to use all that for investment. There ought to be a place for savings no matter how small it's. Something should come out of that $500 for savings. Every investor should be able to set something aside for savings no matter how sure they think they know of the investment they're going into. This isn't even about the famed, "don't invest more than you can afford to lose." Both aren't the same thing.
Good advice and indeed it should be done, because savings will be the main foundation for financial strength,
so that in case of the worst still have savings that will save us financially despite losing most of the money in crypto investments.
I set aside 50% for Fiat savings and the rest goes to investing in crypto and some crypto projects that require capital to work on tasks, airdrops and such.