Intimidation factor is something that cannot be discounted when it comes to finding reasons for success in sumo.
Some of the greatest yokozuna of all time struck such fear into their opponents that many bouts seemed decided before they even stepped into the ring.
For an up and coming rikishi, having to face a yokozuna for the first time is a daunting task. In the case of yokozuna like Hakuho and Asashoryu, not only are they faster, stronger and more experienced than you, but in the unlikely event you earn the win, it's virtually certain you'll be treated to harsh training at the hands of the same man prior to the next tournament.