An honest description leaves the listener room to disagree intelligently.

A description that includes the weaknesses gives the other person something to work with. Once the doubts, the costs and the parts you are unsure about are on the table, any disagreement will be about the real thing rather than about the version you presented. Persuasion that hides those details buys agreement now and loses trust later.

When you next put a proposal to somebody, say what would make you wrong before they ask. It sounds like weakening your case, and it usually strengthens both the case and the decision that follows.