Sometimes you don't have time to unit test. That's okay.

External constraints exists and you may not feel the need for tests in a given moment, as you may think you have a firm grasp on the whole system state and know how changes will ripple trough it.

But I still believe you should feel a little guilty about it. So when things start to fall apart, you will know it's because: "oh, yeah, I'm not testing stuff, let's start testing."

Before that moment, the feel of guilt will help you avoid certain architectural choices that would prevent you from being able to automate code tests later.