The incrementally part is extremely important and often overlooked. I have seen project after project attempt some major big bang rewrite that always takes way longer than expected, delivers less value than promised, and causes problems in areas that used to work fine. We often understand some big picture things better as time goes on but there's a thousand small decisions baked into the existing code that are very easy to overlook

On incremental improvements you should be able to stop what you are doing within a week or two and be ok with leaving the code like that for a long time.