When I was younger, I had terrible impostor syndrome because whenever I tried to use Waterfall, like I was taught at school and college, my big-design-up-front™ always deviated from what the customers actually wanted.
Their needs and the holes in my design only slowly became obvious as the development went on.
When I first heard about Agile, what I was actually being shown was Scrum.
And all the "stuff" that Scrum puts on top of Agile obscures what it's actually about.
It's only in recent years that I've learned what Agile actually is and it's the process that I wanted to employ back all those years ago when I had that impostor syndrome because my Waterfall was crap...
Turns out, it's actually Waterfall itself that was being the impostor.
It's a great pity that I spent 40 years chasing after it and it's only now that, as an aged old git, I can finally get around to doing things the way I wanted to back when I was a pongy little teenager.