Sustainability isn't one optimization, it's thousands. Look end-to-end and take it step by step. Often putting in the effort to understand the full stack, from user experience to data center design or electricity grids, yield simple solutions that significantly improve carbon efficiency. For example, is it worthwhile to spend two weeks reducing megabytes from network communication if the database queries cause 10 times more carbon to be emitted? See Principle 8: Optimization.