My jump from one to two happened when I figured that I needed a road bike to keep my mtb (and all rounder) company.
Since then my little fleet has grown and grown and I currently run a retirement home for old and unloved bikes... in doing that I have to make sure they get out for some regular exercise.
There's a Peugeot that hasn't been getting enough love of late so I'll take her to work today since the day is absolutely splendid and her orange will go well with the colours of the turning leaves.