Earning a living with bitcoin depends on how much food, shelter, clothing, and services costs in your country or area.
I have two situations in mind that will allow someone live by earning bitcoins:
1. The person is living in a third world country. Food, shelter, clothing and service does not cost that much. An individual can support his daily needs with 3$. That is not too much work in bitcoin and also it does not require a lot of investments.
2. The person is living in a first world country. Food, shelter, clothing and services is way more expensive than third world's. The person can support his daily needs either he is working very hard in bitcoin and has a lot of knowledge about bitcoin or he has enough money to invest in bitcoins to get a decent amount of money everyday.
Though the situations are different, in order to make a living out of bitcoin, you have to be knowledgeable about the different ways to earn bitcoin. (trading, gambling, investing, signature campaign or micro tasks)
I am from third world country and I don't think $3 is enough for daily needs, I alone at least need $10 for a day to live in a comfortable way, but it depends on habits and needs of an individual.