The pilot of the twin-engine airplane reported that prior to takeoff, he "didn't lean out the motors". He reported that during the takeoff roll, "there wasn't enough lift and probably the density altitude was involved." The airplane ran off the departure end of the runway into a field, impacted terrain, and sustained substantial damage to the empennage. The pilot reported that the accident was because of "pilot error." The pilot reported there were no pre-impact mechanical failures or malfunctions with the airframe or engines that would have precluded normal operation. ADDITIONAL INFORMATION The computed density altitude for the departure airport was 8,570 feet at the time of the accident. The Federal Aviation Administration aviation safety inspector reported that the pilot was not rated for multi-engine airplanes and that the airplane was not airworthy prior to the accident.