Dies to Removal

A classic mistake that less experienced players make is to value their life total over their creatures and spells. A win at 1 life is no different from a win at 20 life, and, while your life points are just as much a resource as your creatures, they do nothing to pressure your opponent. Take the damage, force him to leave creatures back to block. YP is like the literal best card you could have had in this situation and you allowed him to die.

The upside is that this will serve as a good learning experience.