What you said is not true, ginsan.
discretionary income is any amount of money that you still have after you pay your expenses.
Discretionary income does not need to be fixed or stable.
Sure, it is helpful to have stable and/or fixed income but it is not necessary.
If you say that a person needs fixed and/or stable income in order to buy bitcoin, you are adding an additional condition that is not necessary even if it might be helpful.
It is like saying that I need to have $100 every week to invest in bitcoin, and if I only have $50 this week or some weeks I have $10 and other weeks I have $200, and some weeks I do not have any, and the punchline is that there is a lot of variance in my discretionary income, yet I still can invest in bitcoin, even if those amounts and/or those frequencies are not known in advance.
Bitcoin is all about taking advantage to invest and be profitable at it, this may come by any chance and at any time, for us to be an investor, we may not have to depend on having a discretionary income which some also called a fixed source, instead we can have one or two sources to the income being generated, then plan on the accumulation pattern for our asset and device a strategy to use like DCA, which could best be applicable as at when we are capable enough to buy and hold as the market dips and as we are having our income flow coming.
You seem to not read what JayJuanGee responded to ginsan which you even quoted about the definition of discretionary income. You may have ten sources of income but without a discretionary income. You can also have only one source of income yet have discretionary income, so discretionary income does not depend on how many sources of income you have. What matter is if your total income from one or many sources will be able to cover your expenses and leave you with some balance. It is the balance that is call discretionary income and from there you can make investment in Bitcoin. It is from this discretionary income that you even set aside some funds as emergency funds for things that will require you to spend money which you did not envisage in your expenses calculations but need to be settled. This pattern is for investors that want to go about their investment without running into problems and if you miss it, you will likely not be able to hold for long because which you have issues, you will sell when you did not plan to.