Naptime Trouble

My husband and I are trying to teach our 22 month old son to put himself to sleep. We’ve been working on it for both naptime and bedtime. Whoever is putting him to bed will read a story, rock him for a few minutes then put him in his crib. We’ve been doing this for about 2 months now but Connor cries every time we put him in his crib. Sometimes he’ll cry for a minute, sometimes it’ll be 20 minutes. I guess my only question is, does it ever get any easier? I hate the thought of him crying himself to sleep although I know he’s just mad that he’s in his room alone when he’d rather be out playing. Parenting is tough!