(Eric)Technology always seems simple when it works and it is when it fails that we see how complex these physical and virtual spiderwebs truly are. Networks can fail due to multiple reasons, namely lack of redundancy and failover. This can be in the form of backup servers and switches that can activate when primary hardware fails or backup power supplies for when there are failures outside the network hardware. Hardware runs firmware and software, which needs to be updated. Forgetting to keep it updated can also lead to issues with loss of efficiency or complete failure.
I work for the Texas Department of Criminal Justice, and one of the common LAN issues that we have on our units is outdated hardware. The units suffer daily from bandwidth problems since the physical cables that are run throughout the building(s) are incredibly outdated. This means that the physical network cannot handle the data required for daily business. Another issue with LAN design is the lack of continuous testing. You should plan to test your networks on a regular basis to ensure that they are continuing to function as intended and plan for unscheduled testing after large increases in company growth.