Another #introduction tip for new Mastodon users ( like me ):

Unlike Twitter, which shows strangers' posts in your feed once they get popular or once your friends like them, Mastodon appears to only show you posts by people you're following and posts they've boosted ( which is Mastodon-ese for RT )

So if you appreciate someone else's post and you also want your followers to see it too, you need to click those boost arrows. Just clicking the fave star won't make it visible to your followers.