When we change, we want something or someone to do something differently. It is precisely because we ask others to move away from what they feel is normal and go down an unknown path that this can come across as a threat. The only natural reaction is resistance. It is therefore vital to make every effort to detect and deal with such resistance at an early stage.
An organization doesn't change, individuals do
Suppose a company wants to switch from fixed phones to Skype for Business. On the one hand, this is a purely technical issue with three phases (design, develop and deliver) that can be successfully completed. On the other hand, there is the human side of transition, the users who must also accept and adopt Skype. Otherwise, you as a company have a solution that works perfectly, but the added value of which remains unused. Only when the two sides come together can you achieve the desired result.