I'm on my fifth vehicle in the last five years, for varying reasons.
My long time truck was dying five years ago, so I hurried to trade it in while it still had value. That was a mistake, but not too bad of one. I probably would have come out better if I'd paid to swap the engine. The truck I traded for just had two many issues that became evident after owning it. Sold it four months later.
The next truck was in great shape. Very low miles for the year and got it at a good price, but it was only an extended cab. It worked, but definitely led to more fighting by the kids. At around the same time, I switched jobs and added a commuter car.
A year later I switched jobs again and got another pay raise, bringing a crew cab back into the budget.
I loved that truck and had it for two years, but recently bought some property and the two wheel drive was killing me. Got stuck in mud on multiple occasions. And just like that, my fifth vehicle in five years as I swapped it out for a 4WD crew cab.
I expect to keep this one for a minimum of ten years.