Having a source of income and having a discretionary income are two different things you need to take not off, they are not the same, what is needed to invest in Bitcoin is a discretionary income not a source of income, because their are so many folks that have a source of income but still can't figure out their discretionary income, so if you have a source of income their no guarantee that such person will invest in Bitcoin and be successful if he can't sorts out his discretionary income from there.
Having a source of income is very important in taking care of yourself and your basic needs, but if you can't figure out your discretionary income and you went ahead and invest, you are just gambling, and the end product of such actions wouldn't be pleasing because selling it prematurely will be inevitable.
I got your point, because some people can have this source of income but won't still be able to figure their discretionary income out from their income.
So if I understand you very well, I think what matters is individual commitments to the course or interest to invest, not just the source of income alone, if thats what you meant then you're right.
I think it should now be an established fact that what guarantees your investment in bitcoin is not the amount you earn, it is being able to know your discretionary income from the money that comes into your pocket no matter how small it is then from their your can run your bitcoin investment without derailing from your investment plan, abiding to this, will make you not to think of abandoning your investment halfway since you started with a strategic approach.