There is no problem if we only have one source of income, as long as it is able to sustain all expenses during the month we are going through. Now, if you're going to enter the crypto space, as long as you know how to manage your budget, you can actually do it.
Because there are other people whose source of income is not that big but they are able to save money for things just in case there is an emergency, you have money to draw from that you don't need to borrow money from other people, but the size of the source of income is different; they still have businesses, but they are expensive, so they don't save any money.
Having one income source is better in some cases as I have seen that as more you are earning your expenses will be increasing more. There are numerous individuals who are living their lives only in a single source of income and their life is better than those who are earning lots of money.
Some people have less income but they know how to manage their finances and they know how to save money so they are happy with their lower salary. But still if someone wants to earn money beside their salary then crypto is the best field through which one can earn and that earning amount can then use for investment.