Projects are meant to be diligent, almost scientific undertakings with carefully planned business cases, weighted risks and detailed procedures and governance. But the reality is that everyone is biased and these biases affect the way we see the world, the assumptions we make and the basis for all our decisions. There's nothing 'wrong' with psychological bias, our various biases reflect the lessons we have learned from experience and are the shortcuts we use to help us navigate the world; without these 'heuristics', we'd never be able to cross the road on our own.
The problem with any bias is when it's unconscious. If you know, for example, that you tend to be overoptimistic in your view of the future, then you can make sure other people know this about you or you can take particular care to make sure you have mitigated any risk this may cause.