From the book Simple Secrets for Becoming Healthy, Wealthy & Wise, by David Niven:
'You will face many negotiations in your life - whether for a pay raise or over the terms of a car purchase. Ultimately, your willingness to continue negotiations is based on your own level of self-confidence.
No matter what your other advantages might be, you will end negotiations faster if you lack confidence, which means you'll settle for a less advantageous resolution.
...If you're saying, "Well, I don't know. Maybe. What do you think?" that's not helping. You have to be able to say what you believe, in an unaggressive and uncontentious way. You have to believe it; then, negotiate as if it were true.
Lower self-worth translates into 37 percent less willingness to negotiate and using 11 percent fewer negotiation strategies. Increased self-worth correlates with greater willingness to incur the risks of prolonged negotiation and greater adaptability. In short, the less confidence you have in yourself, the faster you will give up trying to get what you want.'