Whom do you trust? With Office security, as in everyday life, you have to choose whom to trust.
So what's with this trusting yourself thing? You know you haven't put a virus in your macros — so what's the problem?
The issue is that, for stronger security, the Office security process requires you to make a deliberate decision to trust any publisher of certificates, no matter who that publisher is. The process works the same way for all macros, whether self-signed or authenticated. Therefore, you have to choose to trust yourself.
Adding yourself as a trusted publisher is done the same way as adding any other publisher. You'll do this in the practice session.