I thought bf would either work out (great) or totally fail (in which case easy decision to give formula in order to keep baby alive). I really wasn't prepared for it to be continuous pain and problems over 8 weeks (so far).
I had good support before birth, including the advice that yes, practically all women can bf with the right support, but that means you having seen women bf every day of your lives, growing up with hundreds of anecdotes about it, and that knowledge is spectacularly absent in our culture.
The other good advice was "You live in London. There are shops." So didn't buy much before birth. Although this did mean that at 2 1/2 weeks I was in hysterics and packed MrNC off to the nearest Mothercare to get a pump, better pillow, infacol, and 'any other overpriced crap that might help'.
But when I needed help, I spent two hours phoning all the helplines and getting answerphones (in the middle of the day), not finding anyone nearby who could visit, was used as an example of good latching to a trainee HV who had never seen anyone bf before, local bf cafes advertised on the NCT site don't actually exist, and I had enough other problems at the same time that bf just couldn't be my only priority. Mumsnet wasn't much help and reading that it should be possible to bf in all cases just made me more depressed and had me thinking I was obviously a failure and might as well just give up bf.
I've tracked down various bf counsellors etc, but it seems that many (esp online) found bf easy and therefore assume it should be for everyone if they're doing it right. It reminds me of school PE teachers - if you can't catch a ball, you just aren't trying enough. My SIL was the most encouraging one, pointing out that yes her baby was exclusively bf at 5 months, but she'd found it very easy despite doing the same as me, so she couldn't help me as I was different. Stopped me feeling I'd failed.
Everyone I know who's given up bf had thrush, mastitis, and/or gross failure to thrive of the baby, or all-night baby screaming. In my case the pump enabled me to keep giving breastmilk-only for 6 weeks while my left nipple took 4 weeks to heal from a crack. Not sure how long I can cope with thrush though. But at least I'm no longer feeling guilty about on average one formula feed a day and around 7 breast feeds.