A realization on Sunburst, and why he never contacted Starlight Glimmer again.

It all starts with the books the two of them were stacking falling over. Remember the books nearly fell on Starlight. Children tend to either accentuate or minimize the negative consequences. In this case, it means that Sunburst's mind came to the conclusion that he nearly killed Starlight. It doesn't matter that both of them were stacking books. What matters in his mind is who they nearly fell on, and that his perception of himself was of a good pony. And so, out of guilt, he never contacted Starlight ever again.

Which is a sad thing. Think of how much could've been avoided, if it weren't for that one detail.