The opening paragraphs of this article should be a mantra recited by every web developer before they begin their working day:
Fortunately, we as engineers can avoid, or at least mitigate the impact of breakages in the web apps we build. This however requires a conscious effort and mindset shift towards thinking about unhappy scenarios just as much as happy ones.
I love, love, love the emphasis on reducing assumptions:
Taking a more defensive approach when writing code helps reduce programmer errors arising from making assumptions. Pessimism over optimism favours resilience.
Accepting the fragility of the web is a necessary step towards building resilient systems. A more reliable user experience is synonymous with happy customers. Being equipped for the worst (proactive) is better than putting out fires (reactive) from a business, customer, and developer standpoint (less bugs!).