Buffers are Self-Fulfilling

Unrealistic schedules, including worse-case estimates, can occur based on each element.

It is not uncommon for functional elements to build significant extra time into their schedules to account for unforeseen issues.  The feeling is that this approach will help ensure that they meet their commitments.  This is a prudent approach but can lead to unrealistic schedules due to each forecasting element adding their own worst-case, buffered time estimates.  Although some buffered time will be necessary, it is unrealistic to assume that all activities will require all the extra time allocated.  Developing a coordinated, overall schedule with the mutual understanding that some, but not all, activities will require extra time can minimize this issue.