A.S.
Tell him the story of the man who picked up rocks for every bad thing that happened to him. Eventually, his pockets were full so he started carrying a backpack. That became heavy and he pulled a wagon.
As his life became long and lonely, his sore body bent and hunched and tired hands from picking up and arranging piles of rocks, he grew more angry and depressed. A local college heard of this man's massive rock collection and the geology department came down to inspect and study the rocks.
Every room in his house was full, piled high of rocks. Some were little pebbles, others greater in size. He showed them, "this is when a lady cut me off in line" or "this is when I got a toothache and couldn't be seen by the dentist until the next day".
After an entire afternoon of this, the students asked, "okay, now, where are the other rocks?"
"What rocks?" the man replied.
"The rocks you picked up every time something good happened to you?'
The man realized, that he spent so much time and energy picking up rocks for the negative things in life, he never took the opportunity to enjoy anything in life.
-------------------------------------------------------------------------------------------------
So, maybe, after telling him this parable, you can say, "It's fine to talk about things that may be bothersome, but for each negative thing, I want you to think of something good about it as well."