Nelson Mandela once said, "It's always impossible until it's done."
I never knew truly what that meant until the President of the United States echoed the words that so many of us had been saying for years and rejected the "done deal," "no-brainer" Keystone XL tar sands pipeline.
Keystone was a fight that no one thought we could win. When the pipeline was first proposed, every energy analyst, every journalist and every politician either had never heard of it or thought the same thing -- the pipeline was a virtual certainty and its approval was imminent. The thing is they would have been right if it weren't for the people.
This victory was won because of the power of the people.
It started with Indigenous and Metis communities at the source raising concerns about the disastrous effects the tar sands were having on their water supply; their traditional territory; their rights to land and title; and the health of their communities.
It expanded as pipeline routes became organizing maps.
Ranchers and farmers learned to work with Indigenous communities and came together to protect the heartland of America. They carved pumpkins, raised solar powered barns, planted sacred corn and were the first to get the president's attention.
Following them was the beginning of the rise of the U.S. climate movement.
When no one seemed to care, they came to the White House in the hundreds and sat down to protest the pipeline and continued inaction on the climate. Each day they were arrested and yet each day more and more came. At the end of the two weeks, 1,253 people were taken away in handcuffs, and a spark had been lit that would never be extinguished.
In November 2011, 15,000 came to surround the White House. In February 2013, 50,000 went to the Forward on Climate Rally to urge President Obama to reject the pipeline. In April 2014, farmers, ranchers and First Nations rode on horseback together on the streets of DC into the National Mall. And in September, more than 400,000 people spilled into the streets of New York City as part of the People's Climate March.
It was the movement we had been waiting for and its one that just keeps growing.
When President Obama announced the rejection, we celebrated not just because another tentacle of the tar sands had been cut off but because it showed us how powerful people truly are.
It reminded us that when people come together, backed by science and working with justice to push for change, they can indeed move mountains. With Keystone we showed the world that fossil fuel companies can be stopped, that oil profits don't always win out and that the climate is starting to have the voice it so desperately needs.
This victory isn't the end of the road, but our chance to double down on the opposition and one-up the solutions. If we want to take our world back, we need to be the ones to do it. It's up to us to get involved; to work across issues and divides; and build movements strong enough to make the changes we need.
It may seem impossible, but if Keystone showed us anything it is that we are the doers of the impossible.
MORE ON HUFFPOST: