Luma was doing that
A redesigned product page came back without a wishlist, which went on a growing list of things Magento's default theme had been doing for years without my ever asking it to.
I wrote my own login
I spent most of last year building the login for a side project by hand on Node.js, and one Laravel command generated all of it, including the password reset I hadn't gotten to.
Logic in templates
For a year I built tickets like this one around placeholder text and handed the rest to a back-end developer, until the rest turned out to be a few lines in a file I'd been editing all along.
How template fallback picks a file
A 10-minute ticket ate most of a day because there were five copies of the template on disk, I kept picking the wrong ones, and the right one didn't have the dollar sign in it.