I think you are mistaking somethings, what do you mean by any one can invest with any source of income? Any source of income you've once your ready to invest or already in the investment, your dusreatonary income should be traced our or figured out from that your source of income then you can invest with it freely, hey the reason why we keep mentioning discretionary income is because you invest with it freely without at midway of your investment having the mindset of withdrawing your asset, is just like using the amount after you might have finish your other expenses, the left over is what you just need to invest with, bitcoin investment is all about being smart, your smartness and approach while investing in bitcoin helps you to freely overcome some obstacle that might hinder you from accumulating and hodling for a long-term.