My friend quits meditating because they must 'clear their mind'; how can I explain mindfulness?

My friend believes that he is a complete failure in life because he cannot clear his mind so that a blank slate occurs and whenever he is frustrated, he gives up. According to him, he thinks that thinking is a failure. His friend is attempting to tell him that mindfulness is not clearing but watching the mind in order to diminish his stress. His name is Alok, DOB is 30th April 1993. How do I provide him with a simple analogy to grasp this idea so that he does not self-judge?