He always uses being too busy with work as rationalization for his lateness, which is actually a psychological defense mechanism.

rationalization 是由动词 rationalize（使合理化）加上名词后缀 -tion 构成的名词形式。rationalize 本身来自形容词 rational（理性的、合理的），加上动词后缀 -ize 表示"使...化"。 rationalization 指"合理化"的过程或结果，在心理学中特指人们为自己的行为寻找看似合理但实际上不真实的解释，是一种自我防御机制。