How to Plot a Three Book Trilogy

I almost always know how the series is going to end when I start and I find that helps me along the way so I outline the first one. There may be adventures and side stories that crop up that I get inspired to do that I didn't originally plan but as long as I know like where I'm going I find that I can get there too. It's probably a thing of practice too you know my first series though I very much knew how it would end before it began so I don't know if you did with yours but I think it's really helpful because I feel like sometimes you watch TV series and you can tell like it's really interesting they're opening all these loops in