It's not quite an axiom, but it seems like people unused to money who come to have a lot of it, shortly thereafter have no money again.
It's easy to understand why someone who wins the lottery and fritters it away goes down that path, but cash is just as dangerous in the hands of someone who is legitimately disciplined and working hard for their money, putting together good transactions, and building up a base of cash.
Money does all sorts of strange things to your psychology. Here are three big ones:
*It makes you think you're smarter than you are: when you've earned well, you tend to think it's because you're brilliant. You systematically underestimate the effects of market conditions and being in the right place at the right time, both of which can be tricky to replicate without large amounts of experience (and, even then).
*It makes you think you've reached a new level permanently: once you've gotten good at earning money, it's therefore permanently easier. This may or may not actually be true, and almost never to the extent you think with the first successes you have.
It's incredibly obvious, but usually neglected -- you need to spend less than you take in to accumulate cash.
Most people do not give this much (any?) thought, or at least don't take action on it. So, they tread water. Or worse, accumulate debt.
If you're able to spend less than you earn and bank the difference, your cash position goes up. This puts you ahead of the vast majority of people already.
But, then you can wind up in a tricky position.
Especially once you become good with money, you realize you can turn it into working capital at a pretty good rate. Someone who has spent some time learning the in's and out's of a few marketing channels, or technology, or throwing great events, or... whatever... can then turn free cash into useful production, which turns back into cash, at a good clip.