Confirmation bias is the tendency to selectively search for and interpret information in a way that confirms with one's pre-existing beliefs or hypotheses. In other words, you interpret new information in a way so that it becomes compatible with your existing beliefs, and if it can't be interpreted, you either choose to ignore it or call it an exception.
If you believe that prayers are answered, every time you get what you pray for, you take note, and reinforce your belief . When you don't get what you pray for, you either decide more time is required, or more prayers are required and continue to pray. You do not however pause to examine whether you need to question your belief that prayers are answered, even when what you are praying for a long time doesn't happen.
At work, let's say that a manager believes a particular sales strategy will deliver increased sales. Whenever a sale is closed, the belief in the strategy is reinforced, and the sale is quoted as proof of the strategy being right. When a sale is lost, it is treated as a normal occurrence and is put down to the percentage of calls that don't convert into sales (after all, every call and every prospect will not convert irrespective of how effective any strategy is).
At the end of the evaluation period, if the sales increase - then it is treated as a confirmation of the strategy being good. What is ignored and remains un-examines is whether the increase in sales could have been the result of a surge in demand, special one-time orders, special promotions or a range of other causes.
If the sales haven't increased, the lack of increase is attributed to either ineffective implementation, or ineffective teams, or some uncontrollable external factor.
What's happening here is simple - the manager is a victim of a confirmation bias. He selectively processes information that confirms with his belief that his strategy is good, while discarding or attributing extraneous factors to external and out of control factors, and at no time questioning the efficacy of the strategy itself.
Could the manager be right that it's a good strategy even if the sales don't increase at the end of the evaluation period? Maybe yes, and maybe No - we will never know unless the manager actually gets down into a detailed and objective analysis.
There are plenty of examples of confirmation bias all around us in our daily life - at the college, at work, at home and in our interactions with our friends.
How do you avoid becoming a victim of confirmation bias?
Examine impartially information or opinions that conflict with your opinion or belief. Look for exceptions and examine them closely - especially if the issue is of importance. Everyone without exception is a victim of this bias sometime or the other - being aware of it helps in mitigating the risk of perpetuating mistaken beliefs.