I think this is a common challenge that designers face when supporting projects with sustaining innovation goals. Investments and timelines are often incremental in these situations. The designer needs to continually evangelize the long-term vision, while supporting a phased exectution over multi-year timelines. Scope changes and implementation constraints can be very disappointing for a designer. Developing a continuous improvement mindset can provide an internal sense of satisfaction and bolster the grit to keep focused on the small details that add up to a better product. Focusing on product outcomes vs design throughput can also help sustain a designer through long development cycles because the goal becomes something far beyond the design deliverables.