For me, the sad thing is that I had to leave the classroom to learn everything I needed to know about how to teach Maths. There is so much I know now that I wish I had known when I had a class of kids in front of me but I just didn't have the time and energy.
I have chosen to work as a primary maths specialist because I know there are so many teachers who feel the way I used to. The feeling that there are just not enough hours in the day to learn how to confidently teach every concept, to find or make the right resources and always worrying that you are failing your kids.
Now the privilege of what I do is that I can spend my time so focused on one thing and then create, collate and communicate it with teachers who are as overworked and overwhelmed as I once was.