Well ideally bitcoin is a means of investment, but if you really need the money for whatever reason, you have to sell the coins to get some sort of fiat currency back.
You got it right people sell their bitcoins becuse of daily needs and especially for foods and shelter to keep them alive.But the nice of bitcoin was have a capability to pump it's value that's why you remaining bitcoin will higher again.So you don't have to worry if half of your bitcoin will sell it as long as you keep the half as your holdings.