Determination.
Really wanting to breastfeed your child, and only that.
Also you have to be ready to give your breasts to your baby, whenever he/she wants them. This can be hard as you'll feel like a human milk machine some times.
I think for a lot of ladies breastfeeding is VERY overwhelming.. you have to be willing to put your childs needs in front of yours.. you have to be willing to give her your boobs whenever she wants them.
This can be very tough mentally, especially when you're already trying to adjust to life as a new mommy, sleep deprivation, maybe sore nipples, healing from the birth etc.
You have to really want it.. then you can do it!
Even if you bump into problems, get a lactation specialist to help you!
YOU CAN DO THIS!
For myself, the first 2 weeks were tough at times. But she's 3 weeks old now and things are looking better. We're both getting the hang of it more now.
What helped me was my determination, and my husband complimenting me, helping around the house, getting me food/drinks while I feed her etc.
Also knowing she's gaining weight, just cause of me, is awesome and such a boost!