This topic reminds me of the memory stick I lost about 4 months ago.
I usually put it in the front pocket of my backpack, however, one day, when I left for school, I forgot to zip it up. I just left it open. When I arrived at my classroom, I tried to look for my USB stick, but I just couldn’t find it. You know, it is quite small, only about this big. So I guess it just slipped out of my bag.
I was really worried, ‘cause that day, I had a very important presentation to give. The slides my team members made were all in my USB stick. So I doubled back trying to find it. Unfortunately, I didn’t find it. I was terribly sorry, and our study group didn’t get a satisfying grade because of me.
That was not the worst part, actually. The memory is really big, so I basically copy everything onto that stick. It has all of my study materials and pictures and videos from my trips. It’s full of wonderful memories. And I didn’t back up the files onto the cloud. So everything was gone.
This experience taught me a lesson. After that, every time I go out, I would check whether my backpack is zipped or not, and of course, I would have a backup of every important file.
memory stick = flash drive = a small memory device that can be used to store data from a computer and to move it from one computer to another
zip up / zip somebody or something up = to be fastened with a zip/ zipper; to fasten something with a zip/ zipper比如：
This jacket zips up right to the neck.
Shall I zip you up (= fasten your dress, etc.)?
slip = to slide out of position or out of your hand比如：
His hat had slipped over one eye.
The fish slipped out of my hand.
The child slipped from his grasp and ran off.
She was careful not to let her control slip.
slide = one page of an electronic presentation, that may contain text and images, that is usually viewed on a computer screen or projected onto a larger screen比如：
I'm still working on the slides for my presentation.
double back = to turn back and go in the direction you have come from
memory = the part of a computer where information is stored; the amount of space in a computer for storing information比如：
Have you got enough memory available to run the program?
back up = to prepare a second copy of a file, program, etc. that can be used if the main one fails or needs extra support比如：
It's a good idea to back up your files onto a memory stick.
lesson = an experience, especially an unpleasant one, that somebody can learn from so that it does not happen again in the future比如：
The accident taught me a lesson I'll never forget.
We are still absorbing the harsh lessons of this disaster.
It was a lesson not lost on (= learned well by) the team manager.
Let that be a lesson to you (= so that you do not make the same mistake again).
Their openness was a terrific lesson to me.
backup = a copy of a file, etc. that can be used if the original is lost or damaged比如：
Always make a backup of your work.
a backup copy