I very heartily disagree with CC. Why would anyone want to feel alone when they are so upset? They just want their mum or dad, and they cant help it. Leaving them to cry or scream can be very detrimental to babies, and studies have shown just that.

My sister leaves her bub to scream, thinking she will learn. She is nearly 1, and screams daily. I hate it. We have very different children. Mine are happy and content, and her DD screams, cries, and grizzles all the time. How can a baby feel happy, secure and loved if they are left when they most need us???

It can be hard, but eventually very secure and happy bubs will equal great sleep, eventually!!! I always put my babies down while we are singing, happy and relaxed, and they slowly nod off.
Good luck finding the right path for you!!