* We have a lot of automation/tools to prevent incidents when mitigation is straightforward (e.g. roll back a bad flag, quarantine unusual traffic patterns), which means that when something does go wrong it's often a new failure mode that needs custom, specialized mitigation. (e.g. what if you're in a situation where rolling back could make the problem worse? we might be Google, but we don't have magic wands)
* Debugging new failure modes is a coin flip: maybe your existing tools are sufficient to understand what's happening, but if they're not, getting that visibility can in itself be difficult. And just like everyone else, this can become a trial and error process: we find a plausible root cause, design and execute a mitigation based on that understanding, and then get more information that makes very clear that our hypothesis was incomplete (in the worst case, blatantly wrong).