Self Soothing

Why is it so difficult to teach babies to self soothe to sleep? I have followed the instructions to try to set bedtime schedule and routines. However, most people said we should just let her cry it out; all it takes is 3 days or a week to the most for her to learn the skill. The crying time can be from 15 minutes up to 2 hours. I have to admit that I am so weak in this matter. I’m sure Haley is up for the challenge, yet waiting for mom to give her the opportunity to learn. How can I let her cry out from her lung for so long? I can hear her say, "Mommy, Mommy, don't leave me" from her crying. Friends told me I should go do other things like get online, cleaning, or even vacuuming so I don't have to hear her brutal cries. It's so hard! My tears are falling just by thinking about her laying on the crib, rolling back & forth and yelling for some attention. She holds onto the wood panels of the crib with her hands and looks through them into my eyes, just like the prisoners, my heart is broken! I give in again and I have to pick her up and soothe her to sleep by breastfeeding her. Baby, baby, please go easy on yourself and mommy! You have fallen to sleep by yourself a few times with no drama. What if I have to begin weaning you from breastfeeding after you are 1-year old? What should I do then? I guess whatever it takes for you to get enough sleep and be healthy; eventually you will learn, right?