Most change situations involve having to learn something new or doing things in a new way. This means breaking the default pattern of thought that you normally follow automatically and replacing it with a new pattern. For example when you change your car, or the version of Microsoft Word on your computer. The simplest task, that you could do in auto-pilot mode before, takes more effort and takes longer. So naturally there is a dip in performance and it can be very frustrating.
During organisational change, we expect people to take on additional tasks whilst expecting them to carry on delivering their day-to-day work commitments at their normal pace, just when they will experience a dip in performance. This causes unnecessary anxiety and stress.