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.
Discretionary income is highly recommended for investing in Bitcoin because if you invest the funds for your basic needs such as feeding, when hunger strikes, you will remember you have money somewhere, you may not even be think straight at that time. Discretionary income is not the same as fixed income because it can vary base on your cash flow and needs but the main thing is that you need to separate your funds for basic needs and discretionary income and use the later or part of it for investing in Bitcoin.
Doing this makes it a perfect and more convenient way to invest into bitcoin and hold, by using different strategic entry points for an investment and also strategizing on the perfect timing for us to invest on the asset and hold, mostly which is when the market dumps, then we buy to sell when it pumps.
You sound so much like a trader because your choice of words remind me of the time when I was actively trading and ended of spending my hard earned money thinking I will get rich so quick without knowing I would have achieved what I wanted if I just held my Bitcoin without trading them away. I don't regret though because I just see that as a learning phase even though I learnt the hard way.
Now back to our discussion, I want to make a minor correction to your statement on the aspect of the perfect timing for entry into Bitcoin... such thing does not exist and having that mindset can rob you of the opportunity to ever place your buy orders. Anytime you enter the market is always a perfect timing. Just few days ago, Bitcoin made a new ATH which means that anyone who entered the market at any time and any price prior to that time was already in profits, where then is the wrong entry? As long as you have your discretionary income, get started already with your DCA method or any other method you are comfortable with instead of sitting idly and waiting for the perfect time.