In my case......
What helped: DH knew as little about breastfeeding as me (ie - nothing!) with dd1, but had the wisdom to tell me to take one day at a time, was kind and loving, and NEVER suggested throwing in the towel, which would have really shaken my confidence. It took me 5 weeks to get to grips with it but I went on to breastfeed for 18 months.
What hindered: Err... knowing NOTHING, dd's tiny mouth which made latching on really hard, and DH's best friend's wife, who in trying to be helpful kept saying 'you've done really well, don't feel guilty if you stop now'. She'd stopped bf with her first at 6 weeks and never bf at all with her second. She meant well, but I think her advice was more about what was going on in her own heart than about what I needed to hear.