[burnoutgal]

"getting hit for a bus" is a hyperbolic example meant to stand in for a catastrophic event. It really means you (or a family member like a parent, partner or child) has a major health event, for instance. Some things are random, some things tend to become more likely with age. Even just chronic pain or other health issues might make retirement less fun than travelling in your 20s (speaking as someone with chronic pain from surgical implants).

Besides health there's a lot of reasons why being certain about doing something now might be preferable to putting it off for 10+ years.