Surely some mothers cannot produce enough milk, but this is the rallying cry justifying reverting to formula, much as "the baby was too big" is the rationalization for cesarean delivery. Surely it is true in some very small percentage of cases, but it cannot explain away the measured variations and choosing the sub-optimal path. Everyone has their own anecdote, but they can't all be biologically incapable of breastfeeding.
"Concern about insufficient milk supply is another frequently cited reason for early weaning of the infant.90,113–116 One national study on feeding practices found that about 50 percent of mothers cited insufficient milk supply as their reason for stopping breastfeeding.112 Having a poor milk supply can result from infrequent feeding or poor breastfeeding techniques,115,117–119 but lack of confidence in breastfeeding or not understanding the normal physiology of lactation can lead to the perception of an insufficient milk supply when in fact the quantity is enough to nurture the baby.120,121"
Take the CDC's data for example: http://www.cdc.gov/breastfeeding/pdf/2014breastfeedingreport...
When you see breastfeeding at 6 months rates by state that vary from lows in the 30's to highs in the 60's, biology can't explain it away.
And from the Surgeon General's report on Barriers to Breastfeeding ( http://www.ncbi.nlm.nih.gov/books/NBK52688/ ):
"Concern about insufficient milk supply is another frequently cited reason for early weaning of the infant.90,113–116 One national study on feeding practices found that about 50 percent of mothers cited insufficient milk supply as their reason for stopping breastfeeding.112 Having a poor milk supply can result from infrequent feeding or poor breastfeeding techniques,115,117–119 but lack of confidence in breastfeeding or not understanding the normal physiology of lactation can lead to the perception of an insufficient milk supply when in fact the quantity is enough to nurture the baby.120,121"