How can someone rely his own life on a volatile asset like Bitcoin, which is unpredictable on short run? In order to live from Bitcoin investment, this individual has to count on frequent increasements in BTC price, or daily trading. Daily trading is like trading, and Bitcoin doesn't fluctuate only upside. So what is he going to do once Bitcoin suffers a correction?

Everyone needs a plan b, to diversify funds among different investments, so once one of them stops working, there will be others to supply the needs of the investor. It's a basic guideline of financial market to not put all your eggs on the same basket.