One of the first lessons of parenthood--before the child is out of the womb--is that parents are people with vehement opinions. I find it amazing how often someone will dish out advice without stopping to think of how individual babies are even though they all meet relatively the same milestones as they develop.
Therefore, I won't be surprised to receive comments from people on what I'm about to write. There's a method for "sleep-training" babies known as the "Ferber" method--otherwise called the "Cry it out" method. Basically you let your baby scream in the middle of the night rather than go to him until he eventually gets the message that you're not coming and starts going back to sleep on his own. These babies are said to learn to sleep through the night on their own much faster than other babies. (Let me just put a note here that babies who do not get responded to after enough time eventually stop "asking" to have their needs met, which can have very negative consequences in a developing child). Now--for those parents who have successfully done cry-it-out and seem to have well-adjusted children, to you I say bravo! I am not made out of your kind of mettle.
I come from the "attachment parenting" model, touted by Dr. Sears and others. In this method you don't let baby cry it out--at least not alone, and you also don't subscribe to the bs that by helping your baby get back to sleep you are creating a monster child who will beg you to come to his house and put him to sleep at age 40. Around the world families sleep with their babies and answer to their every cry and they turn out adjusted, happy, productive members of society. Only in the US would we worry about coddling our children by showing them too much love. There's a difference between nurturing and spoiling. Spoiling, to me, means never setting limits and indulging a child's every desire when they're old enough to know better. Babies need as much love as you can give them, even at night. They are sponges for love, and the more you give them, the better for everyone.
This brings me to the next big lesson of parenting: Parenting is about sacrifice. The reward is in loving your child and seeing him grow. Sacrifice isn't a bad thing, either. Most of us are who we are in large part due to our parents' sacrifices--even if only the early ones. Even if your parents were terrible :) When you do it for someone you love, it even feels good.