I know this is the most first world problem ever, but I was just thinking about this while repairing something.
Whenever I do things like sewing on a button or sewing part of a seam that's come undone, I always tie a knot at the end of my thread and then start sewing.
However, I remember people from my childhood who always said you should never tie a knot, and that the "proper" way to do things was to make a couple of repeat stitches on top of each other so that it holds. I remember when we did embroidery at school with that binca stuff, there were at least two people who were horrified that I tied a knot to start.
Well, sod those people. I'll tie a knot if I fucking want to.