Probability and possibility isn't the same. The possibility of a very rich person becoming poor is real, of course it's real, you can get poorer, but probability is lower. How many people in the world had a 1+ billion dollars networth, and became poor? Like ended up with under 1 million dollars networth by their death? I can tell you that not a lot, so that means if you are rich enough, you will never be "poor", you could be less rich, but never poor.
Before anyone can get rich, he would have planned his life to that point apart from people that win the lottery or got some quick money through scamming or other illegal ways. The ones that merit the wealth had a plan that they followed and the plan will involve having different investments that they got through diversification. With diversification, they can't go broke that quickly, they might lose some amount of money but they'll be able to recover with the other business or investment that they own. The possibility of a poor man getting rich should be higher than the possibility of a rich man going broke. The rich have well planned life and will not take risk that can make them lose all their wealth. Any rich man that lost everything out of no where would be lying and only filing for bankruptcy as cover up, in trying to avoid the federal government investigation into their wealth.