The question is usually asked in relation to one of two contexts.
"Why did we succeed?" or "Why did we fail?"
Answers to both questions should include reasons. Reasons provide information that can be used in the future to either succeed again or avoid failure. Reasons are shared. Reasons provide lessons. Reasons make us better.
Only one of the two questions ever gets excuses - "Why did we fail?"
Excuses try to cover up reasons. Excuses are selfish. Excuses attempt to share (or deflect) blame. The only thin learned form excuses is to avoid teaming up with the excuse maker.
Failure is not the enemy. Allowing excuses to satisfy failure is.
Ask "Why?" five times. Get five reasons. Clarify your mission, define your core values, develop your mantra.
Ask "Why?" five times. Get five excuses. Update your resume.