This is a non realistic reply, as if optimisation is something that can be tacked on after. The truth is you have to walk the fine line between performance and

This is a non realistic reply, as if optimisation is something that can be tacked on after. The truth is you have to walk the fine line between performance and maintenance. It's good to plan ahead and be able to optimise on the bigger picture early, so the design can go through several iterations and code reviews and therefore be trustworthy at the end. Your example of caching is almost basic programming, maintainable code also caches values after calculation for use elsewhere. You don't not cache the results of a database query and pass it around, that's just spaghetti. In reality you have to break out your design into components that can later be rewritten one at a time in order to eek out performance. Easier said then done, but at a high level this first means keeping your big areas (UI, database queries, File IO, networking) separate, and work out the infrastructure from there.