Humans are good at hoping terrible things will not happen yet
This I have learned from life. It is a very common human mistake regarding coming terrible events. We do realize bad signs. We do realize what is likely to come. Often, we do not get surprised by what is happening. But we are very frequently surprised by the timing. When the unwanted terrible thing happens, we think it came to soon. We did expect it, just not yet.
Do not spend time to worry in advance for a thing you cannot affect
This is likely some kind of good mental defense. A good advice is not to worry in advance for something you cannot affect. This common built in mistake, to expect things to happen later, is a good way to live up to that advice. Without that ability to misjudge and postpone worries, we would be spending a lot more time taking more of the pain. Taking the pain at least twice (before it happens, and when it happens).
I saw the signs, but I did not expect the timing
I did see the signs of my cat Simon coming to age. I did talk and think about it. Yet, when it was time, it still happened unexpectedly early for me. To a part this was a positive effect of this common human misjudgment. To a part it was an effect of Simon's behavior. He did not wait until he was too old. He waited until he was old enough, and then just like he fought for so many other things he wanted, Simon fought to die. This made it all happen very fast. The step from signs of him coming to age, to the step he was dead was a very short time span. 6 days before his death, he was still a happy cat, eating well, running in and out many times a day.