Fragility of Judgement

I love this term, which I just saw at radar.oreilly.com. Tim O'Reilly blogged about Malcolm Gladwell's talk at an IT conference.

In his overview, Tim points out how much our judgement is swayed by non-essentials -- for example, an increase from 5% to 50% in hiring female musicians when using visual screens and the poor record of ER doctors in diagnosing heart attacks because they tend to focus on predictive factors rather than symptomatic diagnosis.

My question then is what kinds of extraneous factors blur our judgements?