Comfortable
One of the biggest challenges to sustaining success is getting comfortable. Things are going well, everything is working, and it is natural to feel good about everything. It's also natural to lose your edge. You don't see things through the same critical eye, and you don't have the same sense of urgency.
You want to enjoy success, and you have a right to feel good about accomplishments. To keep performing at a high level, you not only have to recognize the danger of getting comfortable, but you also have to be intentional about how to attack it.
Ask critical questions, even when things are going well. Require those around you to challenge something you are doing. I used to tell my staff at Maine to go home and think about something they didn't agree with, something they thought we were doing wrong or had to do better. Don't just let the people around you validate everything you are doing. Study other organizations who do things differently than you do, and see if you can pick up some things that may help you. Take a different approach to off-season workouts for a week. Put some guys at different positions in practice. Find ways to make things different, and maybe make yourself and your team uncomfortable, when things are going well.
After six years at Rhode Island College we completely changed the way we played offensively. We had been to 5 straight NCAA Tournaments and back to back Sweet 16s. We were rolling. But I didn't think our returning personnel fit the way we had been playing, so we had to make a change. We went to a more structured offense (something I don't really like) and played off the dribble a lot less. We got the ball to our best players where they were most comfortable. We were a different team offensively, without changing the core of who we were as an organization. We were still tough and competed extremely hard. The change made a lot of people uncomfortable at first, including myself, but it allowed us to adapt and stay ahead of the curve. We won the regular season league title, the league tournament, and went back to the NCAAs. We finished the year 26-3.
It's so easy to be comfortable. Especially when you are winning. But sustaining elite success is really hard, and comfortable doesn't get you there. You have to find a way to keep an edge. I've worked with a number of coaches over the years who didn't see things starting to slip until the results changed. Recognizing your own comfort level and challenging it is hard, but if you don't you'll find yourself in the middle of the pack wondering how you got there.