By categorizing everything manually, rather than using the AutoCat feature (which I see that we’ll get to in step 7), I was reminded that some purchases straddle more than one category, like Costco for groceries and who knows what else.
It looks like splitting transactions is outside the scope of this challenge, but it led me to rediscover that useful feature in the Tiller Money Labs add-on which lets you correctly tune those multi-category entries.