The rating is described as a rating "1 - 10"
But every trick is actually graded 2 to 9. ( https://libraryofjuggling.com/TricksByDifficulty.html )
Presumably no-one ever wanted to define a grade 1, just in case an easier one was discovered, and similarly for 10.
When I was learning to juggle, that was the first step - and for someone who's never really tried to juggle, or toss a ball up and down in a very consistent way, it's surprisingly hard. Honestly, probably not a 1 on the scale.