I guess it's just experience to be honest. It happens rarely, you might be lucky enough to be involved with solving it, and then you focus on the important parts of the project again. I've only worked in startups so don't know about the 'Big Tech' solutions but a little knowledge of general linux sysadmin, containers, and queues has yet to block me :) Once the company is big enough to need some complexity beyond that I assume there's enough money to hire someone to come in and put everything into CNCFs 1000 layer tech stack.

Edit: Thinking on this, if I want to scale something it'd be specific to the problem I'm having so some sort of debugging process like https://netflixtechblog.com/linux-performance-analysis-in-60... to find the root cause would be generic advice. Then you can decide to scale vertically/horizontally/refactor to solve the problem and move on.