You are right. We should not depend our future on bitcoin as its price is volatile. We are not sure on how it will be priced one to two days or years from now. That is why I am just investing the money which I can lose. Those are my extra I guess. But would be hoping that its price would goes up to secure my future. 
Yes, you are correct bitcoin is only my extra job, my extra income I can't depend my future in bitcoin cause we know the value is unpredictable we don't know what happen tomorrow when it down or up. I only invest my a small amount and hoping that my investment will be grow in high profit.