I have been an ardent fan and follower of GMO (as well as you, Jim) since I think 2003 or 2004. I fully subscribed to their philosophy for a long time but changed my mind in 2013 about GMO (but not about you).

What helped is my investment diary where I noted down my thoughts and expectations on market returns and changes to my portfolio in real time. I thought that the financial crisis of 2008 - 2009 finally would put an end to profit margins. I put a note to myself that if profit margins again go back up in 5 years, I might be understanding the whole thing as well as I thought I did and I should not have the conviction on this. Seeing my specific expectations and beliefs fail in real time and over a period convinced me to change my though process and approach.

Dont predict market returns, dont let macro impact you. Those are really the most important lessons from both Buffett and Ben Graham as well.