I think of him when I complain about trifles, ... (Para. 12)
Meaning: I think of him when I express feelings of unhappiness about unimportant things.
Notice how to use the verb "complain". We can say complain about something or complain to somebody. Here are more examples.
He complained about the food to me. (or: He complained to me about the food.) 他向我抱怨饭菜不好。
They never complain about working extra time to anybody. 他们加班加点工作, 从不向任何人抱怨。
When "complain" means "say that one has a pain, illness, etc.", the preposition "of" is usually used. Please read the following sentences:
He went to the doctor complaining of the difficulty in breathing. 他去找医生, 说自己呼吸有困难。
The little boy complained of pains in his stomach. 那小孩直叫肚子疼。