Knowing and doing are not the same thing. This is obvious, but yet we still often behave as if they are the same. We think once we know something we will always remember it and be able to use it, but this is not true. Often our common sense is betrayed by our impulses and emotions.
If you think about your bad habits and disappointments, from eating too much ice cream (despite a commitment to lose weight) to getting angry when your goofy dog chews on your couch (it’s no surprise dogs chew on things), knowledge of these behaviors and a desire to eliminate them may have negligible impact on changing your behavior. Our biological and emotional responses are wired deep within us, and mere thinking differently may have little effect towards behaving differently.
There are many books today about something called cognitive bias. These are documented blind spots in how our minds work, including things like confirmation bias, or the habit we all have of finding one piece of data that fits our theory and then claiming with certainty that the theory is universally true. A wise person would look for data that both supports and rejects a theory as there is often both, which forces thinking about how to improve the theory so it fits the world better (instead of only fitting their private biases).
A meta kind of cognitive bias is faith that knowledge of cognitive biases reduces your likelihood for having those biases. Since most cognitive biases are a side effect of how our brains function, awareness of them is often not enough to change our behavior. But we like to pretend it is. “Oh, I know about cognitive biases, so I’m immune to them now” is a fallacy. As G.I. Joe said, knowing is half the battle. The other half is often the harder one.
Generally we think because we know a platitude we know how to practice it. “Treat others as you would want to be treated” seems simple enough, but as soon as we are stuck in traffic or having a bad day, that platitude goes out the window.
Common Sense is not Common Practice. Knowing is not the same as Doing. It can take months of effort to train yourself new habits for your behavior, work that no amount of knowledge can replace. Sometimes all we can hope to do is improve our humility, as avoiding mistakes and failures completely is beyond us.
Also see: Why it’s ok to be obvious.