Today seems like a good day to talk about heart. It's referenced in martial arts a lot and specifically in ving tsun with idioms such as "The Fist Comes From The Heart.
Heart can mean the will to win, courage, and grit. This can be in a drill, in a fight, and also in your training habits with a drive to improve. Without heart in your training habits, you will never have a good fist - a euphemism for kung fu skill. We've all heard about fighters who have heart. They have that extra drive that pushes them through difficulties and results in them wining a fight against the odds. This is the fighter's heart and it's necessary to excel consistently.
Then there is heart that can be shown during the drills like sticking hands. When playing sticking hands, it's necessary to practice both the competing types of heart above. I say they are competing because if one tries to win too much in chi sau (sticking hands) their techniques will not improve. Their winning heart will cause them to do poor technique that's easier and allows a hit. The poor technique will get reinforced and their overall skill will decline or stop growing. In this case they have less heart to improve (and be sure that improving takes heart).
Finally, heart can mean compassion and love. Without nurturing this heart too, one's fist will not develop well. Practicing compassion towards others helps helps to clear afflictions of the mind such as ignorance, false ego, fear, excessive pride, malice, harshness, envy, & ill will. Once these afflictions are under control the fist's skill will grow and since the fist's skill is growing in the correct manner, life happiness and success will grow alongside it.
So we therefore believe that practicing ving tsun kung fu is about learning how to fight, it's instead about teaching people to have a truly happy life and how to protect that happy life.