Why questions are powerful. They ask for the motivation behind people’s actions. Why didn’t you speak up in the meeting? Why did you tell him?
Why questions have always been my favorite, because they let you get to the bottom of things. In almost all cases though, they tend to have an accusatory tone, pushing the other person into a defensive mode.

For example, ask your boss: Why do you want me to do this? Well, don’t do it. Your boss will definitely feel challenged. Why leads to confrontation, even when you only wanted to understand better.

How and What questions are better while literally asking the same: Boss, what makes you suggest such an analysis?  They invite for more explanation and build empathy without putting the other person into a defensive position. 
By the way, reformulating why questions into calibrating how and what questions are also HIGHLY EFFECTIVE in relationships.

Instead of why do you always come late, ask what makes it hard to be on time. 
Instead of why do you never call back, ask how come it’s hard for you to call me back .

Try it, it will work wonders.