I think it is easier done than said.

1) He may not have understood the mechanics of it. If so, the tree is as likely to fall on you as away from you.

2) Even if he knew what he was doing, there can be endless variables. The tree might not be straight making it difficult to understand how it will fall, there might be wind, the branches could be intertwined with other branches, the tree could be rotted making it break unpredictably, it could bounce when it hits, etc.

-john