How to Avoid Stressful Lessons

I've noticed that my groups of French students are lovely. It's I do enjoy teaching English to French students. We have other nationalities as well in my class. And they've been lovely too, so I'm very lucky. But nevertheless, you do have those feelings. How can I avoid one of those frustrating and stressful lessons? I haven't had one for a while but maybe that's because I always work hard to prevent that from happening. So there's always that sense that you need to be preparing. If you fail to prepare, then prepare to fail. This is true in teaching, but also in everything, isn't it?"