At the initial journey of the virtual world, players only have a few items. They have to collect items during their progress in the virtual world. Some virtual worlds encourage players to collect a whole set of items. For example, a full set of weapons for the whole body includes an axe, body armor, helmet, and shoes. Let's assume there are different axes, armors, helmets, and shoes. When a collection of all four items is mounted on the avatar, the whole performance gains a bonus. Mounting the full set can be a 20 percent bonus over using different parts.
Some other virtual worlds also require collecting a whole set of items to be mixed into one ultimate powerful one. These items are often separated over the whole virtual world. Players have to walkthrough all the places to collect them all.
Players are more likely to stay in the virtual world longer when there is something they have to collect which is still missing. There are several ways in which they can get a new item...