I often joke that my company is "the engineers running the asylum" because there's not much "product management" as a separate discipline; engineering figures out what to do, and does it. But it's not as bad as all that; we are highly data driven, and have a solid A/B test system in place.
So one engineer had a thought that "Subscribe" with a pin wasn't the most clear UI, and that we might get better results with alternate wording. So we took the top bar of this:
The results are often counter-intutive. Stuff that seems like solid UI wins get poorer results. (As happened here - switching to a Bell and "email alerts" from a weird pushpin and subscribe got fewer clicks, and so did trying an email envelope icon and keeping the word "subscribe" ) Or- you might be looking at the wrong result. Like, maybe you don't want more sales leads if they're all crappy leads bumping down the overall conversion rate.
Still, it's good that not everything is just developer or product manager guessing...