In ancient times, skillful warriors made themselves invincible, and then watched for vulnerability in their opponent. Therefore skillful warriors are able to make themselves invincible, but they cannot cause vulnerability in an opponent. The ugly truth is that you can't force someone to be vulnerable. You can, however, sometimes persuade them to weaken themselves. Warfare is the art of deceit.
Players spend most of their time figuring out when and who to trust.
Deceiving your opponent is particularly critical just before the stab. Always have an excuse ready, and try not to make the pre-stab move too obvious. Think a turn or two ahead, and come up with clever and nasty combinations. Naturally, you don't have to worry about this if you have lots of pieces and no enemies. But for those of us not graced with those conditions, deceit is a wonderful way to assist our neighbors in becoming vulnerable.