Guests in this world

In Pirkei Avot (4:10) the verse states, אל תהי דן יחידי . Do not act as a judge alone.
"Matnas Avot renders homiletically, “Do not judge the Unique One (יחידי).” Do not stand in judgment on G-d and the way He runs the world. Lovingly, accept his judgment.
The Chofetz Chaim compared the narrow vision of man regarding Divine Providence to the attitude of a guest at a synagogue. After watching the gabbai assign different people with aliyos(being called to the Torah) he approached the gabbai and asked, “Why do you pick certain people and skip others? Would it not be fairer to go in order, skipping no one?”
The gabbai answered, “Had you been here the last few weeks, you would understand everything. The ones I skipped today had received an aliyah in the last few weeks. Some had a family simcha or the like, and were given the proper privileges. On the other hand, many of the people I honored today have not had an aliyah in weeks. You cannot judge because all you know is what you saw this morning.”
Man in this world is like a guest. In his seventy or eighty years here, one never gets to see the whole picture. Hence it is foolish to think that one can fully understand how G-d runs his world. Therefore let one not try to “second-guess” G-d."

Pirkei Avos ArtScroll Mesorah Series pg. 242

A number of months ago, I read a book by someone who had been raised in a religious environment, but had chosen to veer off the path of Orthodox Judaism. I can, in no way, judge him, as he grew up with an abusive father. I do question, though, his complete ingratitude to G-d. When things were going badly in his life, he rallied against the one Above. But, when things went well, there was no sense of thankfulness. As an example, all during his wife's pregnancy, he was afraid that she would miscarry or that the baby would be born abnormally. However, when his wife delivered a healthy baby, the author's reaction was to have a doctor perform a circumcision days before the eighth day when Jewish people are commanded to perform the ceremony.

Last week, I bumped into a woman whose grandchild was going to undergo an operation in the near future because the child was born without fingers. I remember when my first child was born, I asked, "Does he have ten fingers and toes?" I was relieved when I heard an affirmative answer, but did I thank Hashem properly for a healthy baby? If I was remiss, I would like to take the opportunity now, many years later, to thank Hashem for my healthy child.