YES, Flash Drives Wear Out!
Apparently, many people don't realize this, but flash memory wears out the more you write to it.
How quickly it wears out will depend on the specific flash drive. Like anything, there is a wide range of quality in currently available flash memory-based drives. You can make a rough correlation with the cost of the device, but even that tends to change over time. Depending on usage and quality we could be talking as short as months or as long as several years. Extreme cases of misuse lasting as little as as a few weeks, or on one reported case even a few hours (holding a Windows swap file).
And as many have experienced, when they fail they can fail catastrophically. Just one bad bit or sector in the wrong place can render the entire device unrecoverable to anything short of a complete reformat. Not only will a reformat lose all your data, but it may not work, and at this point you are living on borrowed time - the device will fail again, and probably very soon.
Never Keep Important Data in Only One Place - this applies to much more than just flash drives. If that "one place" goes away, so does your important data.
The obvious solution, of course, is to backup.
Naturally, a lot of people get intimidated by that, because backing up seems big and complicated and scary. It doesn't have to be, but even if it is: get over it or risk losing everything you've stored.
Backing up can be as simple as making a periodic copy of your data on another device. (Emphasis on the periodic, so that your backup stays up to date.) It can also be as simple as installing and using appropriate backup software.