Graduate students often serve as teaching assistants while working on their degrees, and some programs even make teaching a requirement. As a Master's student fortunate enough to have research funding, I hadn't expected to teach during my time at UW-Madison, but I was glad when the opportunity arose anyway (even though it happened during my last semester!)
Tonight, after my students had delivered group PowerPoint presentations on a hypothetical research proposal they developed using data we collected earlier in the semester, I awarded some candy to the group that gave the "best overall presentation" (as determined by class vote). On their way out of lab, some of the students said thank you. After a few "thank yous," I said "thank you too!" The students laughed, and one made a comment about yeah, how excited I must be to grade their presentations. I replied something like "Well, maybe not that part of it..." but said that I did enjoy hearing about all of their different ideas (which was true)!
As a graduate student, it's easy to feel overwhelmed by your relative lack of knowledge compared to the "greats" in your chosen field, so being able to teach some undergraduates about plant water relations and ANOVA tests can be a refreshing break from suffering the symptoms of imposter syndrome. Yes, I do know something! But while I teach my students, I also learn from them. Maybe not what an ANOVA is---they're still figuring that out---but plenty of other things. Even though I'm in the role of "teacher" and they are the "students," the lab sessions I enjoy the most are those in which we both put on both of those hats and try to view the world from multiple perspectives, and all of us grow a bit more into better scientists (and people) because of it.