Our minds can imagine convincing reasons to hang onto things. When we have an emotional attachment to something that is no longer a part of our life, and we question its value, our mind panics and loudly proclaims why we need this thing. It's a protective response. And because it's emotional, it's below the level of thought and not seen for what it is.
It's like a bark from a dog that is meant to keep an intruder away. It's how we sometimes intimidate ourselves. When I'm working with a client, I can feel their panic and fear when this happens. Their eyes lock in place, their breathing constricts instantly, and their body tenses. Plus the voice raises in pitch and trembles a bit. It's an emergency response. That's what it feels like. You can notice it yourself when you are going through your things and you come upon something that brings the clutter busting to a halt.
When this happens, you can think, "Oh, I'm under the influence of clutter." It helps to notice the red flag. If you have the capacity at that moment, you can ask yourself, "How is the presence of this thing making my body feel?" "How does this thing make my stomach, heart and skin feel?" Our minds can rationalize in amazing and award winning ways, but our body doesn't lie. The body states fact.
Check out the body's results. And then ask yourself, "Do I want this feeling in my life?" If you say, "No", then recognize that the item in question is the source of the unpleasant feeling. This insight can loosen the grip you have on the thing, and allow you to let the item go.