Well, consider my restore from this morning.
I had a weekly set in, however it was the wrong weekly set. The restore job required 2 tapes from a previous set, not already loaded in the library - the wizard indicated which ones.
If one completes the restore wizard with the wrong tapes in the library, it starts the tape restore, locks the drive, and sits at 'waiting for tape'.
I then walk to my server room, load the tapes in the library, issue an inventory job, which starts, then sits at 'all drives are busy'.
I must forcibly stop the restore job (or, having foresight, cancel the restore wizard after it tells me which tapes I need) to allow the inventory job to start, then go through the restore wizard a second time.