A result can be unfair and still have understandable causes.

Explanation is not justification. You can trace exactly how something unfair came about, understand every step, and the unfairness remains entirely real. People often argue past each other here, one side describing causes and the other hearing an excuse.

When you explain how something happened to someone it hurt, say plainly that it was unfair before you say how it worked. And when someone explains something to you, you are allowed to accept the mechanism while still refusing the verdict that it was fine.