The thing I wish managers understood better is the more exposure a thing has, the more time needs to be spent making sure it's done right. Spend all the time to architect and get your public API right. One you have consumers, is extremely painful to orchestrate a change if you've some something wrong, which will lead to all kinds of tech debt under the hood.

Then focus on making sure your internal public interfaces are good. By the time you get down to class private implementation I almost don't care how it's written as long as it passes tests. (Hopefully I don't have to say there are a lot of things to care about but they generally are easy to change if you've done something wrong.)

I'm not against agile, but it's worth pointing out that it encourages the exact opposite — get this piece of functionality working and figure out how to jam in new functionality in a later step. You can't architect good solutions only looking 2 weeks ahead.