Most of our application had this same assumption: It's kind a good enough, it should be fine for know. After all it's a Rails application, so the framework will take it over later.
Then, the product grow, the users grow, the processing power increase normal and everything is fine until one day it doesn't. This is the story on how a mature application had our complete engineering team busy for days for an issue that technically will never happen, or when it happen we will are having better problems like millions of concurrent users, but we were not even close to dozens of thousands.
In the code base nothing has been change, the database had no big loads, but our users had a persistent slowness, the reports where about the highest ever? Why?
What is happening? We solved once adding more computers, but we think we can't afford it anymore.