Trying to judge your milk supply is not one of those good reasons, and for most people it's a recipe to undermine your confidence (and potentially your milk supply, if you start stressing out or supplementing in response to unfounded
fears about your milk supply).
But in some countries, such as the UK and the USA, breastfeeding rates drop rapidly after birth, often because of
fears about inadequate
milk supply and other breastfeeding problems.