Most Aikido people say that Aikido is an art of peace and harmony. That's true in a way. But Aikido is also a very violent art in which students are continually fighting. The enemy we fight is as dangerous as they come. It can destroy our relationships, ruin our finances, get us into legal and meidal difficulties, poison us, addict us to durgs or alcohol, and make us into abusers. This enemy knows our every move and every weakness. It, of course, is ourselves.Editiorial by Susan Perry
Aikido Today Magazine Vol. 17. No. 6
While this quote is about Aikido, it's trivial to substitute Shintaido and have the meaning remain the same.
In Shintaido we often talk about changing our partner, but usually the way to do that involves changing ourselves too.