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.
That is true that someone can still live off with one single source of income but that's what he has to do, living within his means. Because if someone is going to live beyond his means and he doesn't have a huge source of income and they're just few, he's going to have hard time supporting that kind of lifestyle. Many become broke because they're too worried about their status and always comparing with the life of others. Forget about people being showy of their lifestyles on social media, don't set it as a measurement of how you're going to cope with life.
There is more to life and just live within your means and be happy with what you have currently. If you can have multiple source of income then that's so much better because you're showing and proving that you can do that and you're a responsible person. Don't live with extravagant and don't be too envied with the life of others if they can get what they want. If you can't get what you want, that's fine as long as the bills are paid and you're getting the needs that are essential for our survival. Someday, you'll be able to get those things that you want but for now, you have to keep on working smart and hard.