I'm struggling to understand the connection between Complexity and asking "why?"

Matt asked: Why is asking "why?" related to Complexity?

Complexity is about their depth, and the why is what gives it to them. So, you can imagine somebody running a marathon. In itself, not all that interesting. So you ask them why? Now, if they tell you 'I thought it would be fun' how much depth does that give them as a character, and is their much complexity to this journey or is simply somebody running for fun?

Okay, so now imagine you ask this running why and instead she says 'when I was 7 my mother got cancer. She fought it, our whole family did, and luckily she went into remission 3 years later. Every year we would go out together in a walk or run for the cure. Sadly, her cancer came back a few years ago and this time it was just too much and it took her life. I'm running this marathon because it connects me to her. I am running because I want to remember her and feel her strength.'

That's complexity. It's her why, why she runs, why this matters to her. And can you see how it offers incredible depth and gives the viewer so much more reason to invest in her journey.