I usually recommend that people have several sources of income but the OP's problem seems to be not so much that he has only one source of income but that it is not enough to cover his expenses. A CEO of a company that earns millions has enough with one source of income, he does not need more, although it is normal that he invests part of that money and generates a second source of income with his investments.
You need to re-evaluate how much you earn and how much you need, some people could live with a single source of income if their salary is higher than the cost of living, but if you are earning a minimum wage then you need to look for other source of income or side hustle to maintain what you need and to have money to spoil yourself or family.
Right but the other side of the equation is to try to evaluate expenses as well, as oktana says. If your salary is not enough, you have to increase your salary or reduce expenses, there is no other, but better if you combine both.