Harry Markowitz, the founder of modern portfolio theory, quote where he says he invests 50 percent in stocks and 50 percent in bonds to prevent regret is amazing to me.Rather than following his own mathematical advice of modern portfolio theory to determine his optimal allocation of stocks and bonds, he instead relies on emotions to guide his decisions. He talks the talk but does not walk the walk in terms of investment decisions.

Please explain the situation from our life where we see someone talk about passionately about doing one thing, but in their own life they do not do it and explain why this happens.