When users experience problems on a network, the root cause of those problems will almost always boil down to three possibilities: user error, software problems, and physical connectivity problems. Although it is a convenient way to dismiss a problem outright and return to surfing of the Web (okay, so not all network administrators sit and surf the Web all day), not all network glitches can be blamed on user error. Software issues on client machines and servers alike can cause access and connectivity problems on the network. Physical connectivity problems such as shorted-out cables, an unplugged hub, or a router with a bad Ethernet interface can also cause problems on the network, and sometimes physical connectivity snafus can be some of the hardest to track down or troubleshoot.
In terms of user error, one way to limit the damage that your users can potentially do to the network is to have a well-informed and well-trained user base. A little bit of well-planned group training for your users can actually negate a lot of potential problems on the network. Some sort of educational opportunity for your users should be built into your overall plan for your network implementation and management.