There are some emotions that feel similar in the body when we experience them but mean very different things. Anger and indignance are good examples. My experience with both is that the energy rises in my body, my vision narrows, my breathing gets shallower and often I have difficulty thinking clearly. My emotion "clouds my thinking" as we sometimes say. So basing my understanding just on the sensations of the emotions isn't a very reliable way to distinguish which of these I am experiencing. Ontologically we say that every emotions is co-creative with a story. That is that is to say that our thoughts can generate an emotion or we may experience an emotion and it shows up in particular thoughts. So every emotion has a fundamental piece of information it is trying to communicate.
The story of anger is that "I believe something unjust or unfair has been done to me or someone I care about". A further element is that "someone is to blame" and my desire is to punish that person. So, in anger I have the desire or predisposition to punish the source of the injustice. The story of indignance is different. It is that "I have boundaries regarding how I will and won't be treated and someone has transgressed those boundaries". For instance someone is speaking to me in a way I consider disrespectful. My predisposition is to "protect the boundary". So the response energy of the two emotions is opposite. In anger it is about punishing another and in indignance it is about protecting myself.
The distinction is profound. Many people I have coached have difficulty being angry or even allowing themselves to say they feel anger because they have learned it is "wrong" or perhaps dangerous. If they are confusing the emotion of indignance with anger then it also becomes unavailable and the consequence is that person will not be able to defend his/her boundaries and thus won't be able to take care of his/her dignity. This can be a tremendous loss and often leaves people feeling less worthy or less important than other people. Understanding the difference can make indignance available which allows the person to maintain their dignity regardless of the situation or intentions of the other person.
In ontological work we say that distinctions are what allow us to see and thereby give us choices. This is a case in point. Without the distinction between anger and indignance we have no possibility of choosing which is appropriate for a given circumstance life presents us.