While freelancing I’ve seen team members being oblivious to how much work would be involved in actually making an area of their product good and not realizing how badly techdebt can compound in the weeks and months ahead when not solved early (usually because “we need to move fast”).
An example would be CSS. Many developers hate writing it and think it’s a trivial toy that even a monkey can write properly. Sure, to get something up and running it takes little effort to get the presentation right in CSS. But making something maintainable that won’t slow down your velocity after a month of adding/removing/modifying rules and class names is an entirely different thing. Yet I’ve rarely met a client that didn’t have a severe tech debt with their CSS – I’m usually not called in to fix that – even those with refined testing and devops processes. Though they usually believe that their CSS is fine.