Bias occurs because we think in terms of a single cause for observed phenomena. Unlike most cause and effect occurrences in our everyday life - failures often require several conditions to occur. For example, a new battery fails prematurely and we replace it under warranty. Our bias is thinking that because the battery quickly failed that it must be defectively manufactured.
In the battery industry there is a saying that "batteries don't fail - they are killed." Proper battery function is dependent upon the charging system, ambient environment and the loads. There are multiple suspects, and often more than one antagonist at work when something fails.
As a mechanic or inspector, approach the problem with the idea of multiple causes or joint action. Round up the usual suspects and keep in mind that there is often an interaction between components. Avoid being overly certain about one's conclusions. As you gain experience you grow less certain because you experience to many "exceptions" to the rule.
