Toughness has nothing to do with it. Neither does talent.
ANYONE can do 8 x 1k at 3k pace. The REST is the difference. I doubt he started at 90s rest out of the blue. Perform 8 x 1k at 3k pace with whatever rest you need. Then gradually work the rest down. With great endurance you can then move down to 90s rest.
Now here's the question for everyone. Is this an anaerobic workout or an aerobic workout....
AEROBIC. It is your aerobic system that determines the success of this workout with such a short rest. Your legs will be heavy. Your muscles will be on fire. Hydrogen will have turned your blood to battery acid. You will have better success in the last quarter of your race because of this workout and workouts like this.