Writing anonymously for obvious reasons. My partner is a billionaire, family has been influencing business and politics for multiple generations.
The “if you need to ask, you can't afford it” mantra really is true.
Don't get me wrong, my partner is not easily parted with money. If about to buy something for $10 and find out online it can be had for $8 it will be put back and bought online.
Having said that, when it comes to wanting something, money is never a deciding factor. If outfit uncomfortable, will just pop into a store, buy and change into new one on the spot. If feels like traveling somewhere, has tickets booked 5 minutes later. Will often eat at the cheap restaurant but the cost of meals OS never a factor.
Meanwhile I grew up always wondering if the extra $1 for guacamole was worth it. My partner was always “do I want guacamole?”
This is most apparent with throwaway purchases, things that lose value upon usage. A home or art could retain value. A failed investment or vanity business could at least potentially bring profit. A $300k car is arguably really worth a few million in unrealized real estate assets. That's why even most multi millionaires, despite being able to afford that Lamborghini, choose to drive a BMW instead. The real reason why professional athletes tend to have fancy car collections is they don't understand the true cost of owning that car is all the potential money from investment they forfeit. A billionaire knows this but just chooses the car and doesn't factor in cost one iota into the decision. An extra million or two won't change their lives so they just choose the car they like.
As other answers pointed out, the wealthy network.
Every social interaction is predicated on who the other person is and what business they can produce. You invite the famous singer to a dinner to try to get them to entertain you. You invite the judge because you never know when he could come on handy. You get breakfast with the governor because you need his support on a new business regulation. You get the number from a mutual friend of another businessman because you both face a mutual problem.
When I first met my partner, I thought this was incredibly snobbish and actively tried to show the error of just viewing people for networking. Over time, I began to come around and see the other side of it. It's not just cold blooded practicality, it's boring to hang out with normal people talking about sports or game of thrones when you could be discussing founding a new insurance company with fellow billionaires instead. They don't even watch sports or TV shows and movies.
Expectations go through the roof
When your family has so much power and money, you see how realistic it is for you to be the same. Like how children with parents that went to college consider that a foundation of life whereas someone who's parents are truck drivers will view college more remotely.
Likewise, the children of billionaires expect great things out of themselves. They'll attend any school they want and have all the financial and networking tools at their disposal. Therefore, while someone like Obama or Clinton would have likely been content if politics failed and they remained wealthy lawyers. George Bush, John Kerry and Mitt Romney would have never been satisfied if they just has moderately successful lives.
This is a big reason for the eccentric billionaires. If you can't lead the world like your parents, then your only other option is charitable work or just being a socialite. No billionaire will ever look upon simply being a doctor as a success unless they are trying to cure cancer. Same with a lawyer unless doing pro bono work. Rule the world, do something noble or just party.
And self made billionaires are a myth. A unicorn if you will. They happen but far more billionaires will eventually come from Marc Zuckerburg’s testicles then all of silicon valley.