How Mother's Milk is Made

An excellent explanation of the most common reason mothers stop breastfeeding (and what helps): not enough milk.
http://www.llli.org/llleaderweb/LV/LVJunJul01p54.html

In a Nutshell: Milk production is continuous and governed by how much milk is left in the breast. If the baby empties about 80% of the available milk, the supply will remain constant; more and it will increase, less and it will decrease. Trouble with milk supply is almost always due to not enough sucking--either too much time between feedings, interrupted feedings or, sometimes, a baby whose suck is ineffective at getting the milk out.