Primarily it is caused by confusion and contradiction in the basic objectives, then content of the offer, ie what product, service or brand says to customers. If you really talk to "its" customers. Although it looks like we have everything perfectly aligned and tested, the thruth can be different.

If we are constantly immersed in a process of the company, we easily may overlook a number of contexts and thus unconsciously divert the vision and goals.

The Causes Are Several 

1)   We fail within the company sufficien and clearl communication, daily routine processes devour us.

2)   We infer from an obsolete and already invalid data and judgments.

3)   The market and target groups and their mutual needs are constantly changing.

4)   Competition doesn´t sleep and endeavour to beat you.

5)   For a long time we think we are doing well and losing self-reflection.