I should also point out that despite being an intelligent parent who knew where to go for help and advice, I still formula fed ds2, because he was in hospital at 6 weeks old, diagnosed as failing to thrive.
He'd lost 10oz from his birthweight (which is quite a lot, if I recall correctly) and at 6 weeks old, still hadn't regained the majority of that weight. I'd had the health visitor on the doorstep every day or couple of days, telling me she wanted ds2 to have gained an ounce by the next time she visited, and telling me to supplement with formula.
When I told her how much I wanted to make breastfeeding work, she told me that she had to think of the best interests of the baby!! I asked her if she thought I didn't have my baby's best interests at heart, and asked her to leave my house forthwith.
I persevered with breastfeeding - ds2 was almost constantly on the breast, and still he didn't gain the weight back, and then one day he woke up from a nap with really raspy and difficult breathing, so my gp told me to take him up to the childrens ward. They diagnosed a chest infection and started him on antibiotics, but what concerned them most was his weight - and they kept us in to see if he would gain some more weight (that's when I heard the staff using the phrase 'failing to thrive' in reference to ds2). In the end, it was only by introducing formula top-ups that ds2 started to gain weight, and then we were allowed to go home, but this spelled the end of bf for me and him.
I can't see how it would have ended well if I had persisted with bfing ds2 - he clearly wasn't getting sufficient nutrition or calories to survive - the intelligent thing was to supplement him with formula, so that he lived. I have photos of him at 6 weeks old, and it is hugely distressing to see this white, spindly baby - he looks almost like a famine victim - and it is my milk that made him that way!
Ds3 was mixed-fed from the word 'go' - he was bf during the day and had a couple of bottles during the night. This worked really well for us, but if I cut down the number of bottles, he just stopped gaining weight.
I cannot help believing that my milk was not any good - I couldn't nourish my own children.