My philosophy and my experience in business is that all answers have their place. The "yes", the "no", the conditional ("maybe","if","when", etc.) and "I don't know." The skill is to figure out when they are best used. Regarding the conditional and the "I don't know" they can both be nearly as powerful as yes and no, if the who?, what?, when?, where?, how?, under what conditions? are rock-solid and informational.