Flash drives are a wonderful storage device as they are easy to use and move around and can hold a lot of data for the size of the flash drive.
Flash Drives are pretty reliable for storage but after about 10 years of the data being on the flash drive it's possible for the flash drive to lose the data or the flash drive become unreliable to connect too.
Flash drives store data through electrical charges and overtime the electrical charges on the flash drive dissipate which means that the flash drive can cause the data to be lost.
So if you have data on a flash drive make sure to get a new flash drive before 10 years and transfer the data over to the new flash drive to keep from losing the data.
Ideally you should have the same data backed up on your computer hard drive, additional flash drives, external hard drives and in the cloud storage.
If the data is really important to you such as pictures or databases that you cannot replace back the data up on multiple devices so you have them readily available.