Irrelevant

On the first glance, it sounds simple enough to understand why having irrelevant or incomplete basic information would lead to slow and biased decision.

But, things are never that easy in real life: How could you know your information is irrelevant or incomplete? Or, in the jargon of Bernard Woolley, how do you know something you do not know that you do not know?

And the opposite is equally true: How could you know you know absolutely nothing that could guide you a better decision? (This phenomenon should be familiar to many medical students. To many apparently difficult question by the professor, the answer could often be deduced from the principles of basic physiology or pathology that one learnt casually in the pre-clinical years.)

The real difficulty is, therefore, in my opinion, not that we have irrelevant or incomplete information, but that we have too much information - and we do not know which is relevant and which is not.

Or, let me modify the famous sayings of Charles Burwell a bit:

Half of you knowledge would lead you to a wrong decision... unfortunately, you don't know which half.