...I have no idea what the "correct" answer is.
This is a common job interview question however, and the best answer is an honest one that you can then spin as a strength by describing how you have since worked to improve.
Mine:
"I tend to be a very hard working type "A" person who expects the same out of others. I had to learn that as a manager my job isn't to necessarily try to turn everyone into duplicates of myself, but instead to guide and inspire everyone on my team to do their best. Every team has A players, B players and C players...hopefully the C's become B's and the B's become A's, but mostly I try to focus on having everyone do their best individually and respect their individual contribution, instead of expecting or demanding everyone mirror my type A personality. The result of this is that I have found the teams I led to be in general happier and more productive"
In general the "I sometimes work to hard and need to occassionally back off and smell the roses" is a good (if corny) answer.