Speaking of design trade-offs, I've found it's really hard to get stakeholders to appreciate the cost of implementing designs. Design cost should be part of the trade-off give-and-take of figuring out what can fit in a release or sprint or whatever, but often all those decisions happen too early in the process to do that. It's easy for one design decision to affect several "stories" and add tens of "points" (in typical agile terminology) to a project, and entirely possible that the stakeholders would rather have five more features than have that widget look and behave just so. Most designers don't seem to consider this much.