Let me make it clear that without a stable source of income it is impossible to succeed in long term Bitcoin investment even if you have a very strong backup funds it will run dry as time goes on and before you no it you will start dipping hands into your Bitcoin investment, nothing can save your bitcoin investment if you don't have a stable income, and just like you said one needs to have a stable source of income before starting his or her Bitcoin investment journey because if you start bitcoin investment without having a source of income and then hoping to find one when you have already started then you are taking a very big risk and is 50/50 you may succeed and you may not so before you start reason all this.
a normal person should not even think about investing with out a stable source of income because after taking a hit for the market the person might lose his mind because that moment he might have taken a big risk by putting all his funds ,and just imagine that happens the person will become forstrated and even start tell other people that bit coin is a scam and that is wrong so it will be more safer to have a stable source of income
Your narration is more like gambling rather than investing, perhaps no one is expected to invest or put in all their funds in to Bitcoin investment, the question why will anyone take a big risk by putting all his funds in to Bitcoin? That's is you are gambling with your investment because it doesn't stand a chance to stay for a long time, a lot of emphasis has been severely made on how we need to approach Bitcoin investment within the comfort of our personal circumstances which includes taken care of our basic needs first and figuring out how much of a discretionary income we have which we can invest with without struggling to sort out our basic needs, that way you will not be frustrated but have a peace of mind you needed to grow your asset, you don't have to put all your money in to Bitcoin investment it is a mindset because Bitcoin is not a quick and get rich scheme but best appreciate it value over a long period of time, you have to decide your funds accordingly to your scale of preference including that which will be use for Bitcoin investment rather than putting all your funds in to Bitcoin. Yeah have a stable source of income is good but it is also good to get started and at the same time be working around improving your finances.