My goal as a leader is to never say "no." Rather even if I know with certainty that "no" is the correct choice, I prefer lead through the situation by considering the possibility of a yes. I try to lay out the best few options that we can see and what the benefits and consequences are from each.
Most choices to try an enhance a plan requires a choice to abandon another part of it. If someone does pose a truly good idea, we'll all probably agree that it's an improvement. If the culture is created that all ideas are considered, then there will be a better chance of good ideas being offered.
If change is always squashed, then ideas for improvement will never be revealed and we will die in status quo…
If an idea is suggested that I know (either because of intuition or previous experience) is a poor choice, I am a better leader if I steer them (be they a subordinate, a peer, or a superior) toward realizing the choice on their own.
Summarized, I'm the best leader when I am optimistic and disciplined enough to choose not to say "no."