Cory - that's a really good point.
BFing didn't work out too well with DS1 - he just wouldn't stay latched for more than a minute or so before coming off screaming hysterically and refusing to re-latch. We had a specialist HV, a specialist MW, a BF consultant and various other people trying to work out what was going on, but there was no obvious physical cause.
The general consensus was that it was just an unfortunate combination of a not terribly plentiful supply, a very slow let-down, and a very impatient baby who wouldn't persist long enough.
We managed to mix feed until 4 months when it gradually fizzled out.
DS2 was BF for nearly 9 months, with a hiccup around 4 months when an undiagnosed tongue-tie suddenly started causing problems (very similar to DS1's) and he stopped feeding altogether. It was snipped and the problem resolved, but the MW who dealt with it said that it was possible that DS1 had also had a mild tongue-tie which wouldn't have helped.
So in DS1's case, BFing wasn't impossible in itself, but exclusive BFing was.
Although to listen to a few random mothers I encountered, apparently I should have just persisted 