Software development topics I've changed my mind on

One more that has opened my eyes recently:

Good, empathetic UI design is invaluable.

Get a professional UI designer. Engineers are (in the main) appalling at it and will cost you time and sales.

In my experience, finding an actually good UI designer is hard.

Obviously they exist, but I don't know how to find them. It seems many — if not most — professional UI designers don't even understand that form inputs need labels.

Got any tips?

I agree, it's hard. I'm lucky that I work for a large org with a separate design department. They are the ones that initiate how our products present themselves to the user, both in terms of styling and user flow, and they spend time and effort researching with guinea pigs what works best. It's very much "Design Thinking" in action. The outcome though is a monumental improvement in how easy the product feels to use. It's an artistic activity and is thus empathetic by nature. Being initially skeptical, I was won over very quickly.