I do not doubt there are people for whom it works like that. There are also people who do not start like gamblers, but end up with an out of control addiction.
I've known people with "get rich schemes" who ended up lying and stealing from their loved ones.
But the self-serving excuse of "I'm only human" is always a lie. That's not being human; that's being a particular, untrustworthy kind of human. Not all of us, or even the majority, are like that. "But it's just my nature" is such a cowardly excuse for lying and cheating.
Fair enough; I certainly wouldn't purposefully hurt anyone (at least not nowadays), and I don't know that I'm willing to extend the benefit of the doubt to Ponzi, but I have certainly done things that have hurt people transitively, or done things that are somewhat self-serving that I convince myself are good for the other person.
I'd like to think I haven't really done anything like that since I was a teenager, but as you said, cognitive dissonance is amazing. It's entirely possible that I do things all the time that are horrible.
It starts off with a small lie to yourself - I’ll just use this money to pay him and when the investment pays off it’ll all work out... and then it grows from there.
Cognitive dissonance is an amazing quality of the human brain. I recommend reading Mistakes Were Made But Not By Me - fascinating stories of how and why it happens.