That applies to me. The only other income I've received was from a clerking job for a trading firm, who themselves subsisted 100% on their trading profits.
That said, I agree with Pabst. In trading you can get situations where you find an edge that makes excellent risk-adjusted profits. You can then really rake it in. A lot of people on the floor were like that - start with a borrowed 10 or 20k, and turn it into 6 figures plus in a short period of time. Or maybe you find a system or method that works great for the moment - e.g. SOES bandits in the early 90s, daytraders in 1998-2002 etc. Generally you find that these "free money" situations don't last for more than a few years. Ok so the floor lasted for over a century but even its time is now up.
Trading is a competitive industry with a rapidly shifting set of rules, regulations, market environments and opportunities. There are low barriers and to entry, and you can easily find that your edge disappears due to competition or changing market environment, and either takes a while to come back or (more typically) doesn't come back at all.
If trading is your sole source of income, and that income dries up as a result of a market change, then many people find it difficult to deal with. The real market survivors are those with the drive and focus to sweat out those situations and apply themselves to finding something new that works in the changed environment. They are the ones that stay as full-time traders for multiple years/decades, until they either make big bucks or get too old and tired to continue reinventing themselves. The rest find they simply aren't psychologically capable of doing this, and so they drift around for a while and eventually find themselves having to go back to conventional employment or self-employment.
You would also be surprised at how little many high-earning traders actually managed to save. Taxes take their bite, and the rest of it gets pissed away on fast cars, powerboats, planes, women, booze, drugs, mansions and 2nd homes, the usual suspects. They assume the good times will continue to roll, and don't plan for the future when things will be different. And as Pabst mentions, if you lose your edge, a million in the bank doesn't pay you much in income.
Luckily there are a few patterns of market behaviour that *never* go away - such as people's tendency to buy tops and sell bottoms due to greed/fear climaxes, or the occurence of secular bull or bear trends in various market sectors from time to time, or inefficiencies in very small-cap stocks, or "can't lose" Buffett-type value plays. However, these opportunities persist mainly because it is difficult to exploit them consistently and successfully - it IMO takes experience and psychological mastery, and/or extreme intensity of research to get good enough at those areas to make it your sole source of income. However, once you do, it will provide excellent returns for a very long time.
So my advice is, if you find yourself with an edge, assume that it will disappear in a couple of years, and prepare accordingly. Try to study one of the methods mentioned above that is likely to persist. From 1999-2002, I was constantly expecting the easy money to dry up, so I worked at different methods that were totally uncorrelated to intraday stockmarket volatility, and kept my spending low so I could accumulate a decent capital base for the future. Each year I would look at my P&L and ask myself why I was bothering to do this extra work when things were so easy, but now it has paid dividends and I'm glad I did it.
Contrast this with many people who hopped on the daytrading bandwagon, and did quite well, but now the market opportunities have gone in that sector, they don't know what to do. They are scanning the job ads, trying to work out the opportunity cost of not getting a $50-100k a year normal job, asking if the stress of trading is worth it etc. They are psychologically ready to give up. Meanwhile the survivors have already changed their game and are scoping out new hot sectors and methods to maintain their competitive edge.
Andy Grove said this about the high technology industry, but it could just as well apply to trading - only the paranoid survive.
