How we change what others think, feel, believe and do
Check the Facts
Bring out some actual data to confirm your point, discrediting the other person's facts or even discrediting the person's character.
Challenge the truth of what is being presented as fact. Question sources. Attack cited authorities. Criticize research methods.
Add new information that disproves that which has previously been taken as fact.
Add emotion to your statement, for example being shocked that the other person has done something reprehensible. Highlight their guilt in some way.
Research well beforehand to allow you to drop such killer comments into the conversation. The higher the stakes, the more time you should spend on digging for powerful information.
Hmm. Let's just check the facts about that.
If I look at what you have actually done, I can't say I'm impressed.
Well, I actually went to see myself and I found that it has not been completed. Why are you claiming that it is completed when it has not?
Facts act as unchallengeable evidence, in the manner of a courtroom, and are far more powerful at persuading than wants or opinions.
Bringing up facts that the other person does not know about or which they think you do not know will surprise them and cause the uncertainty of confusion which you can use to change aspects of the negotiation.
If you can make them feel shame, then they may concede to you as an act of contrition.