It’s our resistance to things that cause the pain.
Even more so when we are aware of something, we know that’s not what we want and then we get angry about being angry, or frustrated about being frustrated, or sad that we are sad and so on. We fight the reaction, we resist the feelings, we try to squash our emotions.
If we give space for our feelings, thoughts, emotions and let them be, just observing and letting it be there, then there is no resistance, no fight and they dissolve without more emotion, thought or reaction.
Philip Dodson 
Very True. But just thinking about stuff which is “best left unsaid”. Is ‘expression’ important there?