The Neighbour and The Wedge.

J-bro cut halfway through this white-thorn trunk, then I tried to finish the cut with the wedge. But as the wedge went in, the trunk started splitting perpendicularly. The more I banged the wedge in, the deeper the perpendicular split got, while the tree still stood. Eventually I couldn't bang the wedge in any more: it was plumb with the trunk. J-bro started cutting from the other side. It was at that stage that the neighbour wandered over. "Would ye not think of banging the wedge in more?", he asked.
There's a moral there somewhere.