Even up to ~5 years ago I was still calling these kinds of things 'unplanned expenses' and then wondering why our annual spend was always 5-10K over what I expected.
But eventually I decided that we are almost always going to spend 5-10K/year more than I expect, which means that our actual annual budget will be 5-10K more than I want or believe it 'should be'. And I plan accordingly.
Now what persists in annoying me is that even when I plan, and can manage these things in terms of cash flow, the universe persistently scoffs at my plans.
E.g., after 3 straight years of out of pocket medical costs (not including premiums) >5K, I decided to use a Flex Spending Account to at least save on taxes! I dutifully set it up last winter to max out (2650$/year) figuring even if we had a more 'normal' spending year, we can carry up to 500$ over to 2019. Well, as of today, we've spent <1,000$ on medical stuff, and I am scrambling to figure out how to burn off 1200$ worth of care in 3 months! I'm actually thinking of scheduling a brain MRI (I get one every few years) an entire year early! Ugh. Good problem to have, I know, but it's so annoying to try to be a smart planner and then have it not work out.
Or, another example: Cars. Our plan has always been to buy one new or near-new car every 10 years, and drive each car for 20 years. That gives us plenty of time to get value out of each car; and it means that we have one car per household (newer car at our house, older car for my mother, who we partially support).
We were on track to ditch our old car (mom's ride, 20 yr old Saturn), give her our 10 yr old Suburu, and buy ourselves a new-ish car sometime in 2019.
But I got t-boned by a college student 3 weeks ago (his fault). His car was destroyed, and our damaged Suburu (back door drivers side crushed) has been at the wrecking yard racking up storage bills while waiting for the insurance claim to go through. After 10 days of renting a car, DH and I figured, 'fuck it' and went down and bought a new-ish car. Which is fine, but a good year sooner than we planned to do it.
Plus, if the insurance company doesn't want to repair our old car, we will now be faced with what to do with the much older car my mother is driving, which we formerly planned to replace with the older Suburu.
It's annoying. On the other hand, everyone involved in the car accident walked away with whiplash. A few seconds difference in timing, and that kid would have t-boned MY seat, rather than the back seat. I was really lucky. So these are first world problems, for sure.
Still annoying, though!