Humans are creatures of habit.
People often move through their lives on autopilot, plodding through the same activities day in and day out. Once in a comfort zone, it can be difficult to change. Typically, this behavior transfers to exercise programs. People tend to get comfortable on one type of machine or in a specific class and repeatedly perform the same routine, on the same days, at the same level of intensity, for the same amount of time, over and over again. Eventually, this can result in exercise plateaus, boredom and even injury.