“Plans are established by seeking advice; so if you wage war, obtain guidance.” True wisdom is tempered by checks and balances, since we are but humans all-too-capable of error and lapse in judgment. The contribution of a plurality of wise and discerning minds is always useful, though the plurality of minds can also make mistakes (the theory of Groupthink). This proverb shows the reasoning behind the elder/committee system in towns and churches, as well as trial by jury.
It also teaches us that the wise person does not act on impulse but only after careful reflection. We’ve seen this before: stop and think; consider alternatives and consequences. Act slowly and thoughtfully, and you’ll be less apt to do things you’ll regret.