Aisin Gioro Hongli 爱新觉罗氏弘历
I just finished watching the 百家讲坛 - 成败论乾隆, here are my thoughts. Hongli is lucky, talented, and hardworking. He sees his grandfather Xuanye and Tang Taizong Li Shimin as role models.
He understands all the reasons that cause previous dynasties to fall. He implements every possible cruel measure to ensure that history doesn't repeat itself under his watch. It appears that by imperial China's standard, he is an outstanding emperor. He became arrogant because he thinks that he is the best emperor. However, the world is changing during his time. The industrial revolution is making the western world more powerful and soon stronger than imperial China. Hongli wasn't paying enough attention to this as he believes that imperial China is the center of the world, and he stands on top of all.
The lesson is that you should never be arrogant and let your guard down. You have to constantly think of ways to improve instead of maintaining the status quo. Disrupt yourself, or someone else will.