Having other sources of income surely makes saving and investing easier, that way one would have enough for their daily expenses and something left for investments. However, there is something i read and i believe it to be true, if you cannot save from the little you earn, you would probably struggle to save even if your salary increases. Many people who became successful investors started investing when they had little, they believed in compound interest and they started very early.
Well, even though it's true that the more you earn, the more you spend, and it somehow feels like your expenses adjust themselves according to how much money you make, and I've experienced this a lot. When I was earning less, we were still doing just fine, everything necessity was easily covered, and at that time, I thought that now if I start making more money, I will easily be able to save because if we are able to adjust within this budget, a higher budget should allow me to have some savings, but no, when I started making more money, it seemed like the expenses have increased, maybe also because of inflation.
Anyway, I think it's not very easy for someone making less money to start saving or investing because you will barely be able to fulfill the basic needs of your household with a low income, and if someone is able to do that, they probably have very low expenses, and definitely have no one else to take care of, because I know that if I'm living alone, I will easily be able to save money no matter how low my income is, but with a family to take care of, not possible at all.