J.J. was about one-year old and had to go to full-time daycare.

He fought it as hard as he could by crying as if the sky is falling. He cried so hard every day at dropoff that made his daycare teachers turned into tears, besides me.

He would cry loud and hard up to an hour and the teachers had to take him out of the baby room for a stroll outside. He wouldn't give up crying until used up all his energy, exhausted and fell into sleep. He did this every day and for more than a month.

I felt so torn to see him crying every day and didn't know what to do to feel less guilty in leaving him at daycare for work.

Until one day, one colleague told me the philosophy about kids crying:

Every one will do the same amount of crying in life. You'd better let the kids do crying earlier, rather than seeing them crying much later in their life. 

Good philosophy. Ever since knowing that I felt much better in dealing with daycare dropoff. And J.J. probably sensed that change as well, and stopped the hard crying the next week. He has been very happy in daycare ever since then.