Today the church remembers Mark the Evangelist – here’s a section from the Acts reading for the principal service:

Barnabas wanted to take with them John called Mark. But Paul decided not to take with them one who had deserted them in Pamphylia and had not accompanied them in the work. The disagreement became so sharp that they parted company;
(Acts of the Apostles, chapter 15, verses 37-39, NRSV)

A bit harsh on his commemoration day to remember Mark as someone who quit, and then was the root cause of a split in the church.
Happily, all was later restored, and perhaps the warts-and-all record should encourage us that disagreements may be nasty, but reconciliation is possible.

This glass is in St. Marks church, Cambridge.