In my experience Ultimate exponentially gets harder as you get better. You go from learning to try and throw the basic forehand and backhand throws, to trying to learn how to throw more and more technical throws. Likewise, on defense you go from shutting your guy down, to having to learn how to anticipate two throws ahead and shutting that space down. I think this is true for most sports. In football, the Quarterback progresses from picking a guy and throwing, to learning how to read space, defenses and going through check downs to find an open guy. When you get to such a high level in any sport, it's then that the mental strength of players is tested. You can be an athlete in any sport and it will get you 90% of the way there, but going that last 10% is just as hard as going the first 90% and that is where it becomes a mental game. You need to anticipate not just one throw ahead, but multiple throws ahead. You need to read defenses and exploit their weaknesses. You need to make a choice and throw the disc, all of which needs to happen in less than 10 seconds. These sequences and decisions need to become muscle memory for your mental game. You need to be focused and you need to trust your team. You are one player out of seven, and your mental strength needs to include the trust that those other six teammates are going to do their jobs. There is no way you can play or win this game on your own, and your mental strength needs to account for that.
For guys who want to get to that next level I would suggest the most work comes in mental toughness. It is so easy to be tired on the field and slow down to a jog, but mental toughness won’t let you do that. It will push you through that natural laziness and tell you that you can rest at the end of the point. How to get to that mental strength level is sort of different for everyone. You need to figure out what works for you, but I think one thing that does help everyone is practicing that focus and mental intensity in every practice. Being mentally tough and grinding out a game is super cool and awesome, but it is more cool and awesome to be mentally tough and grinding in practice. Practice can be the perfect example of something that you do to say “yeah I am ready”. You need to bring your mental toughness to every practice, and then your practices will turn into something actually worthwhile. We consistently talk about that at our BYU CHI practices and often call each other, and ourselves, out when we catch ourselves slacking and faking. We know we need to be mentally intense in practice. It is something that is really hard to do for sure, we constantly have to remind ourselves to do it at practices, but it is invaluable to taking your game that last 10% to the next level.