That's why they make the perfect assassins.
The Institute finds these people when they're young and takes them away for training. But an untrained Nobody is a threat to their organization. And threats must be eliminated.
From Amazon: They needed the perfect assassin.
Boy Nobody is the perennial new kid in school, the one few notice and nobody thinks much about. He shows up in a new high school in a new town under a new name, makes a few friends, and doesn't stay long. Just long enough for someone in his new friend's family to die-of "natural causes." Mission accomplished, Boy Nobody disappears, moving on to the next target.
I wonder if the coincidences are why they rebranded the paperback of Boy Nobody and renamed it I Am the Weapon. Some ideas just float around in the ether.