Mark was against Clark. He never liked how clark treated him. He was always mean even in the office. It led to very strong hostility between the two. They both really hated each other. Nonetheless, mark was a smart and honest man. He knew that hostility is against his rules and that it would hinder his personal growth. This is why, he approached Clark and told him to end the hostility. Clark appreciated the way Mark handled the situation and promised to work on the project together.
Picture is mine.