Oh gosh, it's really too late for me to start on this. Here's the brief version.
BF DS was a disaster. He had an undiagnosed tongue tie (found out at 4.5 months - too late!) and feeding was sooo painful. Everyone said the latch was just fine, but I was in agony. I had to give in to some bottles after only a week, we mix fed with some breast, some EBM and some formula for 3 months then b/f came to an end.
So, second time around my attitude was "well, I'll try it, but I won't beat myself up if it doesn't work out". Ha ha.
With DD it started much better, but she had some of the same issues as DS - refusal to latch on, absolute killer suck, gave me cracked nipples on day one, blah di blah. At 2 weeks it started to all fall apart when she went on nursing strike for two days. I expressed as much as I could, but had to give a couple of bottles of formula.
Anyhow, fast forwarding. Gave night time bottles for 3 months because latching was so difficult and feeding was very painful. Went back to EBF at 12 weeks. Shamelessly used nipple shields to cope with the killer suck and cracked nipples. Dropped these at 14 weeks. I hit many walls, decided to stop b/f no less than 3 times. Now DD is 20 weeks and we're still going strong. 
Now to your question, what made the difference? Well it absolutely wasn't a more relaxed attitude, because if anything I was more hett up than I was the first time around. I couldn't believe I could fail with two of them. I would say I was better informed, I had MN from the word go (found it too late with DS). I also totally ignored the advice about not using bottles or nipple shields and did not accept that it would inevitably be downhill from there - it wasn't. I hate to say it, because I used to hate others saying it - I was bloody minded about it and very very determined to succeed. Most crucially of all - DD did not have a tongue tie. First time around, with the undiagnosed tt, I didn't have a hope really. 