Okay, so before I had a baby I thought, "How hard can it be?" All you do is change them, feed them, burp them, and let them sleep. If they are crying it can only be one of these 4 things unless it is something serious. Of course, if your baby is crying and you don't know why and they won't settle down, yes that's hard. But fortunately the Happiest Baby on the Block book has made huge strides in my opinion of helping me calm her down when this happens.
But okay, I'm sure it will get harder, but so far, so good. However, I do have a word on sleep deprivation.
Before baby, again I was like, "Every 3 hours. That's not too bad. I can handle that. I was up every hour to pee when pregnant anyway." Except, it's not every three hours. Actual sleeping time is more like 1.5, because every time she gets up you're up for about an hour and then you are awake and have to try to fall asleep again, which can take a little while.
To get an idea of what it is like if you do not have children, here's how I would describe it. Take an alarm clock and turn the ringer up to as loud as it can possibly go. Then, have a friend hide it REALLY good--so good it would take you 15-30 minutes to find it. Have the friend set the alarm for 3 hours from now. Then try to sleep. When the alarm goes off, try to find it. If it takes you about 15 minutes to find it, good for you. You now know where it is. Now you have to take care of it again. Call your friend back up and have them set the alarm clock for 3 hours from now and hide the alarm clock again. Be sure you stay awake until after the alarm clock is hidden, which preferably took your friend 30 minutes to do. Maybe try taking a walk. Then, try to sleep again and do it all over again. This is what it is like having the baby cry every 3 hours. You have to figure out why, take care of it, then somehow get to sleep again. You'd be tired and taking naps too!