It is very possible to live and cope fine with a single source of income, what is expected in that condition is to discipline oneself to living within the boundaries of what his income could afford and make accessible to him/her. With a good financial planning a single source income earners could make a better life for himself than a multiple sources income earner who's extravagant and wayward in spending. Life is all about budgeting and planning and when you fail to do so, no matter your sources of income you can't be able to cope satisfactorily well.
It’s not advisable to have a single source of income. It may be possible to live and cope fine with a single source of income but with the rate of inflation, your single income would start to be looking small for and wouldn’t be enogh anymore to keep up with living expenses.
How much you earn would be a good determinant on your lifestyle and even if you earn a whole lot of money, it would start to tell on your pockets later on with the rate of inflation and inflation with the prices of goods and services skyrocketing, it’s advisable to have a second means where income incomes in.
Didn't say a single source is advisable or recommendable to relax on with but in a condition where there's only available source of income a frugal lifestyle can be employed to use for an individual or a family man and it will still go to a great length in meeting their needs even under the current state of inflation right now. Moreover, not all that have two or three sources of income might be earning big put together in total, there are persons with a single income source whose earning could be 2x bigger than some others with a multiple income. The bottom line is that, spend according to your income level and Yu won't have a much pressure to complain or worry on.