Jeff's screwy post reminded me of a recent home renovation.
Finishing off a basement bathroom, I had to connect the shower/tub drain to the roughed in pipe (dirty work, but I got to use a jack hammer so that was cool).
Standing in home depot in front of the PVC pipe fittings, I struggled to visualize how to use the variety of adapters, 90 corners, and angle pieces to make the connection.
Ending up buying a few of every fitting ever made to ensure I had the flexibility I needed when I got back home.
Of course, there are some pieces left over.
Just make sure you keep the receipts for you identity plumbing purchases.