Some people are more sentimental than others. It is not WRONG to be emotionally attached to things, AS LONG AS it does not INTERFERE with your life. For instance, if one never throws anything out because they are attached to it, then that is something called hoarding. If one has no room for what they want to keep, then that is holding onto things by being unreasonably not letting go.
I used to hold onto things until I had the unfortunate task of emptying a deceased family member's 2300sf house, their 1500sf basement and 700sf attic. THAT cured me of holding onto things I no longer actively use. I refuse to put my children and loved ones through emptying a bunch of un needed and unused belongings when I die.
I have two children. One holds sentimental value to all family heirlooms. The other child put family antiques to the curb with a "free" sign when he moved because he could not be bothered with that "old stuff". So, you see, different people have different opinions about belongings.
The nice thing about our minds is that we can remember the good times without holding onto "things" as reminders. If you or someone you love is having a hard time letting go of things, then perhaps they can take pictures of these things as reminders of days gone by without having to store, heat and air condition the stuff while it takes up valuable space in their homes and life.
The funny thing is that we are taught to be successful and buy things that make us happy. These are the very things that become a huge burden to us as we grow and age. Us humans are a funny bunch of people.