Have you heard of tenouchi before? If you haven't you can learn about it at "Terminology: Tenouchi". Even if you heard about it and know about it, please keep reading. That is THAT important.
Are you grabbing your sword correctly? Please check your tenouchi right
now. You don't need a sword to check.
Your tenouchi is to cut not to hit. There is a huge difference.
If you just want to hit a target, your tenouchi isn't really important. But if you want to follow the "the application of the principles of the Katana (sword)", your grip
has to be "to cut", doesn't it?
Check your grip first. Then watch the video below.