DURING THE TAKEOFF ROLL IN THE CONVENTIONAL GEAR AIRPLANE, THE PILOT DIVERTED HIS ATTENTION TO THE AIRPLANE'S FLOOR AND DID NOT INITIALLY OBSERVE THE AIRPLANE VEERING OFF THE RUNWAY. THE PILOT REDUCED ENGINE POWER AND APPLIED BRAKES. THE AIRPLANE EXITED OFF THE SIDE OF THE RUNWAY, ENCOUNTERED SOFT TERRAIN, AND NOSED OVER. HE REPORTED NO MECHANICAL PROBLEMS.