Sure Spelling

I distinctly remember writing in our journals in my fourth grade class and trying to remember how to spell the word “sure.” That word confused me a great deal. It starts with a “sh” sound, so I always spelled it “shure.” I figured it out eventually and I don’t think I’ve made that mistake since, until now. Within the last few days I’ve had to catch myself from typing the H in that word. I wonder why I’ve started doing that again. Where did that come from?