Because the sum of us is greater than the one of us.
If you approach negotiations with an adversarial mindset (believing that it’s you against them) you can’t create more in an agreement than the separate parts of what each of you brings. You both enter into a struggle to win over the other and get the most you can for the least amount.
If you win you will be pleased - at least for now. If you lose, you will want to even the score.
So what happens six months down the track when your contractor is still smarting from being screwed to the floor on price and you want to vary the contract?
You know the saying, ‘what goes around comes around?’ It’s at this point that a poorly executed negotiation will come back to haunt you. At the very least the contractor will play harder this time and give less.
At worst, mediation and arbitration are costly ways to resolve what really is unnescesary conflict.
The relationship counts too
Instead, look at what each party brings and work together to use your combined resources of money, skills, people, knowledge and limitations to fashion an agreement.
If that agreement suits all parties, you have not only created more than you started with, you have enlarged your relationship and made your agreement sustainable over time.
If you need to vary the agreement you should be able to negotiate the changes amicably.
The goodwill makes the whole project less expensive in the long run.
Genuine collaboration also preserves your reputation in the market as a solid, fair organisation to work with.
In a country like New Zealand that reputation is everything.