We shouldn't go into bitcoin investment if we don't have our discretionary income thats the right way to approach bitcoin investment, Investing with money we have to live on is pure gambling and its not advisable to do such, having source of income doesn't guarantee we should invest if we have not yet figure of discretionary, those who Invest with what they can't let go will definitely sell off too soon because they failed to understand not just having a source of should be a guarantee to invest into Bitcoin but knowing you have discretionary income to get started.
You have an interesting point here honestly, because I have seen someone that is working and is receiving salary at the end of every month but he still can't take proper care of his basic needs, reasons that his take home salary is just too poor, so your point is very much valid, if you can't sort out your discretionary income from from your source of income, it's not adviceable to start your Bitcoin accumulation process, because it will be just a matter of time before you fall back to your investment just for survival.
I don't really think Zackz5000 is referring to people that there income is very small to take care of themselves and invest in Bitcoin rather what Zackz5000 was saying is that anyone who uses his or her feeding money or expenses money to invest in Bitcoin is a gambler in a disguise and an Investor is not suppose to do that, zackz5000 further explain that, any money an investor is suppose to use to invest in Bitcoin should come from there discretionary and it is only gamblers that uses feeding money and expenses money to invest because they don't have discretionary and once someone invest outside there discretionary or without having discretionary, it is already a wrong investment