Everyone would love to have a network that is always up and available. The problem is that few people want to design it and absolutely no one wants to pay for it.
There are many ways to make your Network more resilient. Some are necessary for your organization, others would be nice to have and some are overkill. A difficult part is to know which solution goes into which bucket (necessary, nice-to-have or overkill). Then those pieces need to implemented, monitored and maintained.
One example that I have seen at dozens of companies is about the uninterruptible power supply (UPS). A UPS has a battery that is supposed to “kick in” when the normal power source goes out, kind of like a fancy generator. The goal is for the critical equipment to stay alive and the non-critical to power-down gracefully. Most companies have a UPS at their sites but they are not ready for two main reasons, the battery is dead and/or it isn’t cabled properly. Just like any other battery, over time it won’t hold as much of a charge so the battery needs to be replaced.
Another example is if a branch office invests in two ISPs for redundant internet, make sure everyone knows exactly how redundant it is. If both ISPs use the same physical path to the branch office, they aren’t as redundant because the same backhoe will still take them both out. Or if the network isn’t setup for proper failover and failback, then it isn’t as redundant as we thought.
A competent network designer should be able to tell with a high degree of certainty just how resilient the network is and in which ways. Probably the toughest part is to explain to upper management the pros and cons of the new proposal and get their buy-in. Management needs to listen and understand what all the scenarios are and their impact so everyone will be informed and aware of the possible situations. Those meetings are time consuming and can be very boring but they are necessary. The other option is for the engineer to write all this up and email it out but we all know that no one reads anymore.