Read the poem and answer the question.

I quarrelled with my brother
I don’t know what about,
One thing led to another
And somehow we fell out.

The start of it was slight,
The end of it was strong,
He said he was right,
I knew he was wrong!

We hated one another.
The afternoon turned black.
Then suddenly my brother
Thumped me on the back,

And said, “Oh, come along!
We can’t go on all night-
I was in the wrong.”
So he was in the right.

-by Eleanor Farjeon

What is the main idea of this poem?