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 makes you think your time is incredibly valuable, because you're brilliant and you've reached this new level permanently.
These have all sorts of negative corollaries. You'll see people:
*Work less hard, because they've got it all figured out and don't need to work as hard.
*Put less effort into the long-term development efforts that pay dividends far down the road.
*Make quick "good spending decisions" instead of "best spending decisions" -- doing quick calculations and spending more liberally on purchases that seem okay, and not looking to get particularly good prices for things any more. This is easy to rationalize when you think your time is incredibly valuable, you're brilliant, and you've reached a high level permanently.
*Greatly overestimate how good they are at domains unrelated to what they're skilled in.
The last two are what make you go broke. When you're starting out, you eat off the dollar menu. You scrap and save. When soup goes on sale 2-for-1 at the store, you haul 60 cans of soup home on foot four blocks during a blizzard. By ceasing to do that, overhead and expenses grow which chip away at your bottom line and net worth.
That's not what kills you, though.
What kills you is thinking you're brilliant and underestimating the effects of being in the right market at the right time, underestimating the effects of hard work and doing things upstream, and getting cocky... and then putting money into something you don't understand.
That's a bad idea anyways, unless you're willing to outright lose whatever you're speculating with (speculating because, really, you can't call it "investing" if you don't know what you're doing).
The only people I've seen avoid this are people who had a specific, illiquid good investment place to put money, who put it religiously there, and didn't keep too much cash on hand.
"Stay modest" or "keep working hard" isn't particularly good advice -- not because it's wrong, but because no-one follows it. Even among the best and most driven and grounded people I've known, almost everyone falls prey to overestimating themselves and underestimating external and largely uncontrollable market forces in their success at first.
If you accept that premise, then having a lot of money in the bank is dangerous to your net worth. Almost everyone I've seen get there for the first time tends to waste the majority of it. Again, through frugality disappearing and spending chipping away at it partially, but especially through mentally sainting yourself and then making bad investments.
The people I've seen break this trend are people who put their money into something they understand highly well, know the in's and out's of, that is rather illiquid and is regularly doable. Real estate is the most common one, and I've seen people who earn and gain a lot put money into real estate and get cashflows back, hold their properties forever, and not get into too much trouble by having too much cash on hand. There's other possibilities, but you'd have to know them exceedingly well.
So, that's worth considering -- if you think you're at risk of having your cash go away anyways (since it tends to happen so very frequently), you might learn about an investment class and diligently carefully deploy a bulk of your funds there.
Cash in an inexperienced person's bank account seems hazardous. Experience and character building is the long-term answer; putting that cash somewhere you understand very well and can't burn through it might be the short-term answer.