Even due someone is investing in Bitcoin for the short term or the long term, it is advisable the person should have a source of income so that he/she will not rely on selling his Bitcoin holding to solve his life challenges. Fomo can also make someone to sell his Bitcoin holdings because he/she invested in Bitcoin to get some profit in an estimated time but when the profit doesn't come and the price of Bitcoin dips, that person might be forced to sell off his Bitcoin even at a loss.
You're right, some Invested in bitcoin as their one and only last means for financial breakthrough and all minds are on it, what we should have done is to make sure that bitcoin Investment is not the only thing we do, we have to create time and efforts on other assets to complement each other because bitcoin may not be as this always on the bullish and we may needed to sell while the market is unfavourable at dip all because we are in need of money to carter for other things in demands.
Actually there is a saying that putting all your eggs in one basket is a very risky one because if anything should happen to the basket all the eggs are gone, so relating it to what you are saying, however you are correct because as an investor or a business man is never an ideal to have only one single investment because if anything should happen to it, you will be hit back starting from square one.
So as a bitcoin investor in as much as bitcoin is one of the best and reliable investment I will not encourage someone to have only one source because we know it takes a longer time before seeing a profits on your bitcoin investment since you are holding.
So perhaps having other source of income will serve as an appetizer that will take care of your daily needs while your bitcoin investment is up and running.