I'd start from the fact that Nicolas I was not supposed to be an emperor. His elder brother Constantine should've, except secretly renounced his claim to the throne in 1823. Very few people knew it and Nicolas was not among them.

After the death of Alexander I, Nicolas proclaims Konstantin as an emperor in Saint Petersburg. While at the same time in Warsaw Konstantin abdicates the throne.

For short period of time Russia even had a coin with Konstantin I on it and part of the army even swore allegiance to him. Which was also a problem.

Anyhow - Nicolas was never taught of how to be an emperor. He has his strong sides (in international politics at least) but in the end this played a bad joke on him as he became overconfident. At the same time he ruined his own army by paying more attention to the looks instead of read education and improvements. He also managed to build the vertical system of yes sayers similar to the one Putin has now.

All of this led to Crimean War (yes, also very similar to the current situation) which led to many reforms later. Including freeing serfs, local governance etc.