I think an aortic aneurysm is what took out John Ritter.

He was in terrific shape, and just dropped dead.

I know someone else that was also in great shape (AT through-hiker), and died of a brain aneurysm. They found him dead in his RV, in Vermont.

We all have today, and right now, is the only guarantee.

I also know folks that have very bad quality of life, yet somehow, manage to have a great attitude.

I think strictly speaking it was an aortic dissection that killed John Ritter, not an aneurysm. Aneurysms grow slowly, and like a balloon, the wall thickness goes down as the vessel circumference increases. So then it can suddenly leak. The aneurysm is chronic (though often asymptomatic), the leak is usually sudden and catastrophic. An aortic dissection is a sudden tear in a usually non-aneurysmal aorta, if the leak goes all the way through it's usually immediately lethal, but often the pressure of blood "dissects" (separates) the inner and outer walls of the aorta, leading to all sorts of weird symptoms, which is why it is often misdiagnosed (A vascular surgeon was once reported to have said about aortic dissection that the "the standard of care is to miss the diagnosis", because it so often mimics other conditions, both benign and dangerous. )

As I recall it, Ritter didn't drop dead but generally, absent any preexisting context, aortic disection is a tricky differential diagnosis and so in his case they chased the wrong dx for a few hours until the window for intervening had closed.

Grant Imahara from Mythbusters is another one. 49 and in ostensibly great health, taken out by an aneurism. Life is short, at best, but for many of us it will fall shorter even still.

Ultimately we're all made of meat, and sometimes the meat goes bad.

Got diagnosed this year with mitral valve prolapse. It won't be an issue medically for some time, but it is definitely sobering to feel the heart beating so strongly.