If it sounds simple, you’ve done your job.
That’s your goal, by the way — with your teaching, marketing, presentions, website, and product itself. The complexity is there, of course. Complexity is always conserved. You’re solving hard problems.
Does your audience understand you? Do they also have the problems you are solving? Can they see themselves using your product? Does it feel right to them? Does it sound simple?
The superpowers of famous physicists like Einstein, Feynman, and Sagan was their ability to make us understand it. To make it sound so simple.
When you’re able to make it sound simple, that’s when you know you really understand it yourself.