Please help me, I'm new to shaving underarms?

Your armpit hair doesn't grow in just one direction, it grows in all sorts of directions. That's why I shave my armpits up to down, then down to up, and the left to right and right to left. This way you get all of the hairs that grow in all different directions. That hair probably didn't come off because it was growing in a different direction than you shaved. I don't think it matters what time in the shower you shave your armpits but I guess I do it in the middle of my shower, idk why thats just when I do it. After a while of shaving your armpits you'll get used to it