Why do I feel numb apathy when sending Metta to neutral people like strangers?

As soon as the guide requests me to wish a person, whom I am not hostile to, such as a colleague or a cashier, loving-kindness, my mind becomes numb. I am not angry, rather, my wave of boredom and apathy is extreme, and I begin cogitating over my grocery list. This is a bewildering block of neutrality. I am concerned that I am unable to get emotional energy with strangers and therefore lack compassion in general. What am I going to do to convert this block of emotional apathy into real emotion? I am named Sunil and I was born 5 th August 1993. Time: 1:40 PM. Location: Nagpur.