I mean I see rails perform horribly too, it's my job to go in and fix things, and I focus a lot on fundamentals (what's your DB doing, what data do you need to serve the request, what shouldn't be inside of the request-response cycle).
Because a lot of web developers these days build applications and ORM's are great but make certain patterns convenient so it's really easy to code yourself into places that don't scale. Then people reach for various caching solutions rather than taking a step back and looking at what's actually executing.
I've seen just about every bad pattern you can imagine and it's not usually obvious because the code looks simple enough. Like that permission check in your controller is actually serializing 1000 ids and querying against them, or that .first doesn't have an index so you're sorting the whole table, and much worse than that.
