In other words, we have to recognize we have a duty to takes certain actions. This raises the question of how we know what action is right. In other words, there is no such thing as situational ethics. The maxim is that it is wrong to lie. Most Kantian thought involves rule deontology.
Kantian ethics work best when they involve language and speech.
They begin to fall apart when actions are involved. In other words, they can be defended when talking about lying, but when talking about, say, stealing or killing, the appeal to reason begins to fail. The reason is that speech can be shown to be contradictory, while with actions, this is not necessarily so. Acts are judged on by their consequence. The distinction is how others are affected.