Until you actually begin turning thought into something tangible/testible, you don't know what works (and what the actual bugs, issues, and important details are)

If you think about something and then do it (kind of like the old waterfall method) you come to every problem with a solution you crafted in your head before actually diving in, and by the time you do dive in you realize your solution isn't the best but have no time or space or energy left to incorporate a better approach

A problem that stops you and requires a day of thinking is one that needs to be approached differently so you can make progress every day. We don't know how many days we have left, don't think all day today and do nothing, leaving that for tomorrow.