Theory:

It is common for brothers and sisters to quarrel, although sometimes they may not even be able to say why they quarrel. But how long do such quarrels last? How do they end?
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.
 
                                  Eleanor Farjeon
Reference:
National Council of Educational Research and Training (2006). Honeysuckle. The Quarrel (pp. 39-40). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.