Here's a handful of stuff I'd like to add.
1. When you're a kid you have no idea that mailing a bill payment immediately makes four new bills materialise in your mailbox.
2.There are localised black holes in everybody's house. You've met them - they're what happens when you put an item down someplace and then, an hour later, you go back to that place for it and the thing is simply not there any more only to resurface in an entirely different spot a month afterwards when you no longer have any further need for that thing.
3. If you own cats it is impossible to ever leave the house again without cat hairs on your clothes.
4. Choosing "safe" (i.e. meaningless) combinations of numbers and letters for your passwords will inevitably lead to your being locked out of a vital website at a crucial moment.
5. A corollary to #4, putting things away in a "safe" place usually results in your finding a place that's safe even from you. Perhaps especially from you. Perhaps this is related to the localised black hole issue.
6. You generally DON'T have that extra carton of chicken broth, extra tin of beans, extra package of coffee, that you thought you did and were counting on.
7. You're supposed to KNOW when something you put in the oven is "done", even when the recipe gives you no hints.
8.Time is this timey wimey wibbly wobbly thing that stretches interminably when you are waiting for something but slips through your fingers like sand when you need more of it.
9.You will always have extra batteries in the house... in EVERY size except the one you currently desperately need.
10.The last time you are certain that you know EVERYTHING, you'll be about seventeen years old. After that, if a message on a computer screen asks you if you are SURE you want to proceed with something, you will generally start twitching (unless you're a certified techie in which case please make your own set of rules).
11. Instructions on putting together kits into useful objects are never helpful in that task. Even if they have pictures. ESPECIALLY if they have pictures. And there will always be a screw or a nut or a bolt which you have no earthly idea of where to put. Oh yeah, and you will always find yourself at a point where you require three hands to do something which the instructions refer to as simple.
12. It is practically impossible to open certain kinds of jars. Some manufacturers go wholly overboard in their understanding of "vacuum packed".
13. Childproof caps, on anything, are an abomination to people who don't have children (and would really REALLY like to get that headache tablet out of the bottle before their head explodes).
13.Staying up until midnight loses its magic when you HAVE to do it, repeatedly, to meet a deadline.
14. There will come a time when you tell somebody that you "slept like a baby" - but actually meant that you slept all night in snatches of fifteen or twenty minutes at a time punctuated by an hour of insomnia in between.
15. The phrase "you can't miss it" in any given set of directions usually means you're in the next COUNTY by the time you realise that you HAVE.
16. Sledding down snowy hillsides is wonderful. Driving on ice sucks.
17. At some point in your life you will find yourself with a new stapler and a whole box of staples which only fit in the OLD stapler which broke yesterday. Life takes a particular joy in presenting you with mismatches at critical times.
18. Machines are programmed for someone else's best case scenario. No amount of yelling or resorting to cold logic will convince your printer that it still has ink in the cartridge - you KNOW it has - if its manufacturer has programmed it to insist that it does NOT.
19. You will eventually learn that the word "nice" does not mean what the dictionary says it means, particularly if uttered in a certain tone of voice or a certain context. In fact, you will eventually learn that a lot of words can mean precisely the opposite of what you thought they did when thrown at you in general conversation.
20. You WILL dream of the Only True Way to Save The World. But you will never remember your dream when you wake up in the morning.