I think that you have hit upon an interesting point made in the book. Jesus really did not go around grumbling and complaining all of the time. However, many so called Christians go around with a sour expression, gossiping, and complaining all of the time.
You would have to refer to the Gospels of the New Testament for the details regarding the life and teachings of Jesus. He taught, ate, walked everywhere he went. He is attributed to have healed blind, crippled, and leprous infections. He is attributed to have turned water into wine, fed 5,000 persons with 5 loaves of bread and 2 fish, and other things.
Jesus had a moment at the tomb of Lazarus, his best friend, just before he is attributed to have raised him from the dead. The scripture records: "Jesus wept."
Jesus was most angered by the money changers who were buying and selling livestock just inside the temple. He flipped over heavy wooden tables and drove them all out of the temple with a small whip made of rope.
For the most part, as I have read the gospels, I have gotten the idea that Jesus lived in the moment and attempted to teach his followers to share what they had with others, do good deeds and kind acts, and to be respectful in the House of God. Jesus encouraged his followers to trust God for everything they needed rather than be selfish and greedy regarding their possessions.
I really don't get that Jesus grumbled or complained. I do get that Jesus encouraged others to stop grumbling and be more appreciative for all that they had.
"Stop grumbling among yourselves," Jesus answered…….. I am the bread of life. Your forefathers ate the manna in the desert, yet they died." John 6:43-49
Matthew 25, beginning with verse 34: "Then the King will say to those on his right, 'Come, you who are blessed by my Father; take your inheritance, the kingdom prepared for you since the creation of the world. For I was hungry and you gave me something to eat, I was thirsty and you gave me something to drink, I was a stranger and you invited me in, I needed clothes and you clothed me, I was sick and you looked after me, I was in prison and you came to visit me.'" This shows a life of service.
But read what the righteous say: "Lord, when did we see you hungry and feed you, or thirsty and give you something to drink? When did we see you a stranger and invite you in, or needing clothes and clothe you? When did we see you sick or in prison and go to visit you?" The righteous simply did all they did without noticing that they were doing good deeds but out of the fullness of knowledge that they were followers of Jesus.
"The King will reply, 'I tell you the truth, whatever you did for the least of one of these brothers of mine, you did for me,'" and they were given eternal life.