What Is One Small Course Design Change That Improved Learner Engagement?

I'm always looking for practical ways to make e-learning courses more engaging. Recently, I've been experimenting with shorter content sections, knowledge checks, and interactive scenarios.

For those who build courses regularly, what is one small change you've made that had a noticeable impact on learner engagement or completion rates? Was it related to course structure, visual design, interactions, accessibility, or something else?

I'd love to hear about real-world experiences and lessons learned.