Lack of Knowledge
This is not the users fault, if you do not know the capabilities or features of SharePoint you don't know what it can do and how it can benefit your work life. You might see SharePoint of a hindrance or harder to use then the method previously used. Take a shared drive for example if a user is used to finding document in one location and now told they are going to be in another location without know the reason why or how it can help them then they are going to be resistant. But if they are shown or told that SharePoint has a great deal of options that make it a better spot to store documents over shared drives (versioning, approval, workflows, checking documents out, retention policies) just to name a few then they are more likely to embrace the change.
Making employees aware of all the features is also important they might know that they can store documents but are they aware that they can create dashboards, manage projects, communicate with team members, create blogs, and create communities again just to name a few things that SharePoint can do. If your employees new the all the capabilities they would see that SharePoint in conjunction with office is your one source for keeping and displaying information so that everyone in the company can work together no matter if they are in the same office or they are half way accost the world.
The last point that I have is that the employee may know the capabilities but the company is not effectively communicating why they wanted SharePoint in the first place. What is it trying to solve or what was the purpose or scope of SharePoint. Is this going to be used companywide? Are we replacing another system with SharePoint? Are we trying to get information to our mobile sales staff, possibly setting it up so they can access this information on the road with their mobile devices? Each of these things mentioned above will help an employee envision and feel that they are a part of something rather than something that someone is pushing down their throat.