"Robert's Rules of Computer Order" joke
You will never have an extra blank disk.
If you do bring along a blank disk, you won't need it.
If you don't bring along a blank disk, it will be the only available opportunity to obtain a copy of a hitherto unattainable and uniquely appropriate program.
If someone else is watching while you are doing anything on the computer, anything at all, it will screw up (that's a technical term).
The percentage chances of screwing up increase in direct proportion to the size of your audience.
No matter how simple it seems to you, your explanation will be more than they want to know.
You will amaze yourself at how much you know.
You will amaze your mother at how much you know about computers.
You will always have one disk envelope too few. Or too many.
The only pieces of data you will ever lose are the ones you were going to save just as soon as you finished typing a couple more lines.
The update of your program will use the keys for something entirely different in this version than it did when you first learned it.
You will not understand it the first time you read it in the manual.
You will understand it better the next time you read the manual. For no discernible reason.
When you are late for an interview and need a last minute copy of your resume your printer will go down. It will always go down. It doesn't care. Nowhere in your repair manual will it ever tell you what you really need to do, which is to turn the darn thing off and get yourself a cup of coffee/tea.
You will never know what a user file is.
The price of anything you buy will stay the same until the actual impact of your money on the bottom of the cash drawer, at which time it will automatically re-list itself in next Thursday's paper at 30% less.
Staring at the screen for 97 continuous minutes will not necessarily reveal to you the secret location of any colon that should have been typed in as a semi. Or vice versa.
It will always seem like your friend got a better deal.
The 800 number will be busy.