This is an easy one to start off with. The tale behind Tom Bakers infamously long scarf is no secret. The original designs for the costume simply showed that the Doctor needed a scarf of regular length. A lovely lady known as Begonia Pope was hired to knit the scarf and was delivered a selection of colours of wool to choose from however when the production team arrived several weeks later, the poor woman had used all of it! The scarf went around Tom Baker several times, but the production team decided to keep it. During the Tom Baker years the scarf began to get longer in accordance with Tom Bakers wishes. It seems the knitting bug was addictive. The production team may have tried to imitate the same success with Colin Bakers costume, which dramatically backfired and turned out to be one of the most criticized features in Doctor Who history. It just goes to show what a delicate balance there is between the overdesigned and the serendipitous.
