Therefore, do you think that a source of income must be steady enough for years, before one can be financially free or rich or very wealthy, depending on the source(s) of income?
Your sources of income determines how stable you will become and becoming wealthy has a lot to do with your level of financial, how well you have invested your money and the assets you have acquired that will keep your finances flowing, if you do not have a stable source of income or an investment that brings you good and steady profits how then can you consider yourself as a wealthy person. Your sources of income determines how wealthy you have become if you do not have good multiple sources of income you can not enjoy financial stability and become rich will be difficult for you because there's high rate of inflation out there having one source of income ma never make you rich.
That is what most people aim to do in reality. You have a certain amount of salary, hopefully rising per year for inflation reasons, but also you could get promotion and earn more too. And then, you save some of that for investing, and you hope that your investment income passes your salary one day. This of course isn't an easy path and most people will fail doing it, and "breaking the piggy bank" will happen more often than people desire to. In the end, its a good move and we should all try to do it, no matter what the end result is, the goal is good and the path is good and we should attempt it at least. Even failing and cashing out means we have done something good in the end, we helped ourselves short term at the very least.