This is something I hear from new parents A LOT! And its usually followed by 'the only place they will sleep is on me or their father/grandparent/etc'.
Believe me when I say that I was asking the same questions just over 3 years ago when my daughter was born. I had been working as nurse in a neonatal unit for 7 years and I thought as long as a baby was well fed, warm, and wrapped up like a spring roll they should sleep for at least 3 hours at a time.
Oh, how wrong was I!