Lots of things are obvious in retrospect or when pointed out but opaque before then.

And some things are obvious to you and amazing to others http://sivers.org/obvious

Yes but.

Imagine yourself as a user of this service. You sign up, get the "email confirmation", think everything is good. A day later you notice that it isn't working, check up, actually read the email and click the link.

Now you want to report a bug. What do you say? How do you explain that you got it to work, but it could have worked better? When there's a large helpdesk, this kind of feedback is nearly impossible to give in any meaningful way. Even if you could speak to the coders concerned, often it's hard to get them to think in a different way and see the problem.

So it's obvious but it's hard.

Possibly, but like many things that are "obvious" they seem not to happen as often as you'd think they should.

In hindsight. The problem is often that we as programmers name things after what we use it for internally, or where we want to end up. Ie, we want an email conformation, but the customer that has to send it, so please do.

There are a ton of things that are obvious once you think of them.