Strange how our brains work. I’m a lefty who can’t write or throw a ball right handed but if I played golf or cricket my stance would be right handed. When I started tying, without thinking about it, it was naturally right handed as well.Yep - I mean I am left-handed, as in Jimi Hendrix, John McEnroe, Leonardo da Vinci, etc.
My set-up looks like this from my side...
I know a few fellow lefties who taught themselves from books where the instructor was right-handed and they simply followed the diagrams and ended up tying right-handed. Maybe that includes you?
The implication for tying flies left-handed is that a lot of threads have a twist in them that tightens when wound right-handed, but unravels and splays apart when wound left-handed. You can see the thread splaying a bit in that shot - and that is one of the better ones for lefties - Uni 6/0. Given the choice between struggling with splaying thread on my fingers, and using a bobbin holder, I still prefer to struggle with the thread.