There will always be a reason behind everything, especially when it comes to people.
No matter who they are, there will always be something driving them to do certain things—even when it seems like there was no reason at all. A lunatic kills because it's fun, a crazy person kills because of something only they could see, a good person kills—because there's no other choice, and a tyrant kills because he can.
One might say they kill for no reason at all, but that's a certain.
It was the nature of humans to use their minds to make a reason out of anything.
Regardless of how obscure, there will always be a reason.
Just like Master Tobias, he must have a reason behind doing what he did to them.
But a reason could wane over time.
Since Master Tobias persisted for years upon years, concealing his true intentions while quietly steering others down the path he wanted them to take, the reason behind what he did must come from within. It had to be personal.