What did Jekyll say his worst fault was and what was difficult about it?

As you can see in the quote below, he believed his worst fault to be the fact that he never denied himself pleasure. Unfortunately, some of those pleasures were an emnarassment, things that weren't approved of, and were in fact looked down upon. Thus, he hid things from people in the hopes of retaining his good name.

"......the worst of my faults was a certain impatient gaiety of disposition, such as has made the happiness of many, but such as I found it hard to reconcile with my imperious desire to carry my head high, and wear a more than commonly grave countenance before the public. Hence it came about that I concealed my pleasures; and that when I reached years of reflection, and began to look round me and take stock of my progress and position in the world, I stood already committed to a profound duplicity of me."

Nice.