I mean, in this situation if the market will come down then obviously the trader/investor will panic trade. And will face loss too. So, to keep your mind relaxed and to avoid yourself from all the market sentiments, a source of income is necessary. It's not that compulsory but I would say it's the best practise to have a source of income before investing in BTC or any other currency.
Only those success stories that we heard off, but again, there are tons of people who lost and were not able to succeed. It is really better to have security first, like your job or other source of income that can make you survive even if your investment fails. You should plan it out like plan a and plan b so that if ever the plan goes wrong, you can still fall back, rather than only having one plan, like only investing, and not knowing what you will do if your investment isn't successful.