The concept of Sunk Cost is simple: It’s money, time, effort, energy spent that have already been incurred – and hence cannot be recovered. It’s your past successes and failures.
To make the right decision moving forward, the past has to be looked as Sunk Cost. Never get emotionally attached to the past even though you have given it your all. Make the right decision moving forward without the pressure of recovering your past investments, time, effort and ego. This simple concept will allow you to discover new opportunities, and achieve greatness without the weight of the past.
The past is a teacher, but the past is also SUNK COST.