People usually attribute one, or sometimes even two, reasons for an action.
"Why did you do this?" => "Because of XXXX."
It makes the explanation easier to digest. It provides a narrative. A neat story that we all love to hear.
But reality is so much different. Every single thing that happens, happens because the whole universe conspires that it happens. This is not a bold claim, this is simply scientific fact (sans the conspiracy part). We call the parts of the past universe that caused the present the "light cone", and it grows at the speed of light. In theory everything that happens on Earth is affected by everything else on Earth except the most recent hundred milliseconds or so.
But even if we're not talking about the raw, physical level, the single cause narrative also breaks down. People do things for multiple reasons, and very often there is not a single critical reason for a decision, but rather multiple factors all contributing to it. In fact, it can be easily shown that any decision that rests solely on one rational reason is fragile, since if upon further inspection the premise does not hold, the rationale becomes invalid, and the decision will be a wrong one. It is a better situation to have a decision made because all indicators point to it being the right one, but none of them being critical or decisive in its own right.
So when asked "Why did you do this?", the answer is not a neat and tidy story. There is no grand narrative except "this is the will of the universe". Some call it God, the Tao, 天, whatever.
It is the recognition that we ourselves do not make a decision without cause, that makes the decision powerful. The recognition that all that we do is backed by the power of the whole cosmos is such a powerful thought, yet people cling to the idea that perhaps one single egoistic thought could be a reason for a decision or event.
I still love neat and tidy stories, but the same objective event can be told in so many different ways. Reality is the sum of them all.