What was once useful and important to us, later becomes an obstruction. It's not that this thing, person, or activity became bad, it just no longer has any use for us.
Initially we can have some resistance to letting it go. Our mind and heart floods with memories of the time it was beneficial. It's like a powerful lobbyist, inside our heads, defending the item. But the resistance is a red flag. It doesn't feel good. It's an indicator of the actual effect this thing is having in our life now.
Clutter busting is seeing the true colors of the effects of our things. It's getting past what we think something is for us, and seeing the thing for what it is.