The Executive Chef at a hotel that I worked at. He showed off to me once. He took an onion, peeled it very quick like, and then took a good quality paring knife and diced it up with 1/4" dice incredibly fast and perfect. I could never do what he did. He was also very good with ice carving. He carved a swan once using his chisels. Outstanding. Not something I could do. He worked at it for a few days in the walk in cooler. It stayed pretty much frozen for that time period.
The chef used to make us dice within certain tolerances. Ex.: 1/4 inch dice, or 3/16 inch dice. Some stuff just got chopped in the chopper.