So basically cluster B personality disorders produce more cluster B personality disorder. A finding that certainly lines up with clinical experience.

You'd probably agree there is almost always more than one logical / rational next step to consider, right? Decision making in chess is about weighing different probabilities, long-term outcomes etc. How do you decide that you've reached the most sound conclusion? How do you reach a conclusion at all?

The unconscious part of that decision-making process lies in the moment just before you determine you've made your most sound decision. While you were circling through different options, at some point your unconscious brain decided it knew enough, and converged on a decision. This choice has been shown to take place fractions before you become consciously aware of the choice. If a neuroscientist were reading out your brain signaling while you were playing chess, they would know you've reached a decision right before you yourself would know you'd reached a decision.

No, but your brain will have decided on the next move a short time before you became consciously aware of it.

While you are weighing different options and strategies for your next move, at some point you will reach a critical decision threshold - when you feel like you accumulated sufficient evidence for a certain move to give the "go" signal. You will reach this point first unconsciously, then you will consciously rationalize to yourself why you make your decision now, after the 15 mins, and not for instance after 14 or 16 minutes.

Think about it, when you decide on your next move, what made you so certain about that move right then? What caused you to go over the tipping point from contemplation to action? Most people will mention that at some point they just "know" they are ready.

It helps us to rationalize and therefore explain our actions to others. Which is hugely important for us as a social species. Basically we act first unconsciouly, then come up with the reasons for why we acted that way, then convince others of our reasons while believing ourselves that these were truly our motivations.