There is a reason why so much artwork - particularly older, valuable pieces - is displayed behind glass cases or out of the public's reach: the art is easily damaged and galleries and museums don't want to take unnecessary chances with their investments. When you are a private collector, those safeguards aren't always maintained. This isn't a problem when personal collections are small, but it is when you own a $140 million dollar painting, such as Picasso's La Reve, owned by Steve Wynn. Wynn, after selling the painting for just under that price, accidentally punched a hole in the canvas with a careless elbow.
Apparently, the painting can be restored and Wynn is taking this as a sign that the painting should not be sold, but when you're dealing with something so valuable in the first place, even private collectors might consider an extra precaution or two.