If you ask somebody why they did something, you’ll get only justification and very little useful information.
Generally speaking, in a conversation, if you ask your buddy Joe why he started a fight with Alvin, you won’t get much useful information. The human reaction to having motives questioned is often an automatic marshalling of justification. Joe might say, for example, that Alvin had it coming and that Alvin had been bugging Joe for a long time.
On the other hand, try using an alternate wording. Instead of asking why, try asking “what led you to …” For example, you’d ask Joe “What led you to get into a fight with Alvin?” In this case, often his answer will be somewhat different. He might say, for example, “I don’t like him much, and when he stuck his finger up my nose, I lost my temper and hit him.”
Asking “why” is usually a waste of time; asking “what led you to” generally provides a better picture of what happened.
Knowing this important secret of the universe, go forth and prosper.