The effect works because our brains need to conciliate the fact that we are helping someone with our dislike for them, and the easiest way to do that is to assume we actually like them.
The request creates a contradiction and then discomfort for the person who dislikes you. And that pushes one to readjust their way of thinking.
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Cognitive dissonance makes our mind try to protect our self-image and the connection between our thoughts and actions by modifying our opinions.
Once the justification or new opinion arises, we become more sensitive to any information that supports it. We also get more skeptical of any information that opposes it.
It suggests that holding 2 or more contradictory beliefs at the same time causes people to experience mental discomfort, which manifests as psychological stress.
And people will always seek to minimize their cognitive dissonance and the discomfort it creates.
Ask for help when you need it, but not too often.
If you reach a roadblock during a negotiation, ask the investor or negotiating party for a favor and give them a reason to come back to you. This will help you reopen the discussion, and give them a perceived sense of power you can use to your advantage.