I think it may be safe to assume we've all known someone who seemed to blend into the background, and let the world go on around them with little confrontation. It's not that they didn't want to participate but perhaps they where scared, much like a slug or snail retracts from being confronted by a single touch, wallflowers are introverted in a similar way. Wallflowers are delicate by nature, though you may over look their existence because of their shy nature, they are perhaps the most interesting people to get to know because of their unique perspective. They have observed many things in their years of living, and have the ability to build a great understanding from their surroundings and the people they may encounter. Many have a heightened awareness and an open mind for new ideas, which is more than an average person could say for themselves. Much like a slug takes it's time to go from place to place, wallflowers take in all they can about their surroundings and enjoy the simple things about life. They don't tend to overlook the little things, so often times they go about things in their own manner and get lost along the way. Which in this case, is often never a bad thing at all.
If you ever find yourself in the presence of a wallflower, be sweet and understanding. It may take time and patience but it's often times worth all of that. In taking the time to nurture a friendship with a wallflower you have the amazing gift of watching one fully bloom in front of your eyes.