We stop looking for new and exciting things and become complacent with that which is in front of us. We become too tired, or too afraid to engage. Understandably, if a person has enough bad experiences they will be slower to want to make another attempt. Conversely, when you start to experience success, you begin to uncover more and better things, faster, and easier, and you want to do it more. Success breeds success.
Fear can be a crippling emotion.
It can dominate our thoughts constantly if we allow it. Oddly, most of it is based upon dealing with the inevitable fact that no matter what happens, death is certain. This is a topic we avoid because it makes us uncormfortable, but it is the avoidance of it that causes discomfort. To a certain degree, what we are doing, or should be doing on this earth, is trying to prepare for a dignified death. It is natural to default to a life that is frivolously allowed to pass by, considering that, after all, we know our final fate.