Once committed (completed), the results of a transaction are permanent and survive future system and media failures.
If the airline reservation system computer gives you seat 22A and crashes a millisecond later, it won’t have forgotten that you are sitting in 22A and also give it to someone else.
Furthermore, if a programmer spills coffee into a disk drive, it will be possible to install a new disk and recover the transactions up to the coffee spill, showing that you had seat 22A.