How do you explain the last sentence written by the protagonist of Butterfly Effect 1?

"If anyone finds out about this, it means that my plan didn't work, and I'm already dead. If I can go back to the past, I'll save her." How could he explain this?
There was more. In the end, Doctor Hei said that there was no diary at all. Was that true or false?
Was the protagonist's transmigration all his imagination, or did he really transmigrate?
(If what Dr. Black said is true, then it should mean that the main character is imagining things. It means that the main character is mentally ill like his father. If that's true, then how did Dr. Black know that he had transmigrated?) Like a broken arm or a mother with cancer.)

I hope that those who have studied this can give a logical explanation- -

Answer 1

The last sentence written by the protagonist of Butterfly Effect 1 was:

Even a small flap of a butterfly's wings could have a huge impact thousands of miles away.

This paragraph was describing how a seemingly small incident could cause a chain reaction and lead to serious consequences. In the novel, this incident was an experiment that the protagonist encountered while exploring the butterfly effect.

In real life, the vibration of butterfly wings is indeed a small matter, but if we don't consider it carefully when dealing with it, it can also cause serious consequences. For example, a wrong decision, an irresponsible behavior, or a small social change could trigger a chain reaction that would affect the entire society.

Therefore, the meaning of this sentence was to remind people to always be cautious and think when dealing with things. Don't underestimate every detail because they may become the source of a bigger event.