This has certainly been my own experience in life. My step-father was a very studious and responsible person. He worked 30-years from the age of 19 with the state as an HVAC service tech until he retired at 49yo with a full state pension, and then went to work for a private company. His plan was to earn as much as he could until he turned 55, and then retire to live/work on the small farm he and my mother had just purchased. Everything was coming together, his new job placed him in a senior project management position, and gave him a considerable salary compared with the state.
Shortly after he turned 50, he was diagnosed with pancreatic cancer, and he died several months later, following a very painful and difficult attempt to treat it.
In my mind, this kind of thing is the height of tragedy—he did everything right. He exhibited an incredible amount of self-control and deferred his happiness, ensuring that his family and finances were well-cared for and secured, and then having fulfilled his obligations, he was almost immediately robbed of a life that he’d worked so hard to earn.
I experienced a few more object lessons in the same vein myself, namely having been diagnosed with multiple sclerosis at the age of 18, and readjusting my life’s goals to accommodate the prospect of disability. I’m thankfully still churning along under my own capacities, now at 41yo, but MS can be unpredictable, and I find it is necessary to remind myself of this from time to time. I am grateful for every day that I have, and to the extent it’s possible, I try to find nearer-term sources for happiness and fulfillment.
Don’t waste any time planning for more than the next five years (with the obvious exceptions for things like financial planning), as you can’t possible know what’s coming. Even if the unexpected event is a happy one, like an unexpected child or sudden financial windfall, your perspective will almost certainly be dramatically altered 1-2x each decade.