Air is invisible but it is amazing what difference pumping a bit more into your tyres will do. Because the tyres are the link between the bike and the road, they are a critical part of the interface and a small change makes a big difference. Cue metaphor: … and that reminds me of programming.
I can spend hours refining a script so that it is tidy, efficient and reflecting all the current best standards in programming for the language in question. What really makes a perceived difference though, particularly to the people whose desire for functioning websites and information systems is ultimately paying my keep, are the critical points where good decisions will make my systems easy and pleasant to use.
Sometimes it is important to attend to things that are less obvious (back to the bike, you might not realise a cable is fraying until it snaps) but, in every project, I try to give sufficient attention to figuring out where the rubber hits the road.