Master Chen mentioned in the last workshop about the concept of 45 degrees. He was referring if there was an incoming energy directing at you at 45 degrees, one way to react would be to push at 45 degrees w.r.t to your body. Doing a rotation would be the same thing.
Here is my understanding after thinking about it:
The outgoing energy will be perpendicular to the incoming force. For the rotation part, a tangent of a circle is always perpendicular to the centre, so it is the same thing.
Earlier today, I was doing some gardening at my backyard. I had to create a flower bed, so I needed to remove some existing grass. I was using this half-circular flat shovel usually used to create a nice edge. At first I was using it perpendicular to the ground, trying to cut through the grass and its roots by hammering it or stepping onto it. It didn’t really work. The shovel wasn’t sharp, and a fair amount of the force going down to the ground was bounced straight up back to my hand. By accident, one of the hits landed at 45 degrees to the ground, and on impact, the shovel slided across horizontally, and it worked much better like a knife this way, and my hand didn’t feel any rebounding force. I believed that this could be explained in physics, however, the more important point was that Master Chen demonstrated something quite similar before.
You push on something in one direction, and since the hand couldn’t get advancement, it went to a different place.
I found this taiji thought during gardening interesting.