My first boss made me sketch every detail on paper for a month. It felt painfully slow, but I still catch myself doing it for tricky parts. That old habit probably saved me from a dozen dumb mistakes.
I mean, the "simple idea taking twice as long" thing @the_sam said is one way to look at it. Maybe it's just me, but taking a bit more time upfront can actually save a ton of time later. You avoid having to go back and fix stuff that wasn't thought through. I'd rather get it right the first time, even if it feels slower at the start.