Why clinging is a problem

The following paragraph is from a little article called "The wisdom of surrender" that I found over on the Wildmind website:

Clinging, or holding on, is simply the attempt to stay with those things that we think are sources of happiness. Ultimately this is fruitless because everything changes. If I see a new relationship or a material object as sources of happiness, I’ll suffer when that relationship or material object change — as they inevitably will. It’s not that I can’t enjoy these things: in fact I’ll enjoy them more if I don’t cling to them, because I won’t be surprised and disappointed when they change.

It also helps to remember that what we are inclined to think is a source happiness probably isn't.