At 15:33 on Wednesday, the Philae probe, part of the Rosetta mission, became the first human craft to land on a comet. Moments later it took off again. It hadn’t completed its mission, and it hadn’t intended to leave: it had just bounced.

After a ten year journey through space, travelling over 6 billion kilometres, costing the European Space Agency over a billion pounds in a venture that took a quarter of a century to plan, the Philae launcher was flying away from its destination almost as fast as it had approached. Tethering harpoons never fired, and rather than snaring its White Whale (which is sadly shaped more like a duck) the lander had simply glanced off it.

It rose a kilometre from the surface, a long way for a comet smaller than Cambridge, and had it been travelling a few centimetres per second faster, it might have been lost forever. It bounced once more before settling, possibly in the shadow of a cliff that will prevent its solar panels charging. We most certainly have landed on a comet, but whether or not the mission has been a success is up for debate.

But there’s an even bigger question here. Was it worth the risk?

I believe this is still a victory. We will get back some fascinating data about the chemical make-up of this comet, which will shed new light on the theory that the water needed for life on earth came from comets, and possibly even that comets are the catalyst that set life into motion on earth in the first place. The batteries have now died, and only a fraction of the hoped-for data may make it back to earth, but this could, and should, stand as a stepping stone on the path to more advanced and more ambitious missions, and that is worth its weight in rocket fuel.

Plenty of people will see this result only as the disaster it could have been. Depending on how we look at it, this it’s either a sign saying 'Yes, it’s possible. Do it again. Go further, go faster, go bigger', or it’s a warning to 'Go home'.

We weigh up the costs and rewards, the chance of disaster and the promise of progress, but these chances are not known, these costs cannot be so easily quantified, and eventually we have only our ambitions and our anxieties to judge by. It would be all too easy to sit on our hands through fear of failure. But we should be letting our sense for adventure, and our will to improve ourselves and our condition, lead our decisions.

In our lifetime, we have seen work at the leading edge of scientific progress stagger to a halt from fear. Concorde was retired in 2003 not because it was inherently unsafe, but because public perception had turned against it. Instead of a futuristic vision of how small we can make our world, we increasingly saw a wasteful, undesirable, extravagance. Three years ago the last space shuttle flight touched down, and what once promised to be an ever-improving programme that would make it easier for mankind to leave the earth had become expensive, dangerous and unnecessary. We have pushed the envelope of human ability and then paused, stepped back, like a child learning to walk who takes their first few steps before getting scared, faltering and falling.

Then last month a Virgin Galactic spacecraft, the poster child of the next generation of accessible space flight, crashed, killing one of its pilots. Many will have lost faith in the project thanks to what appears to be a tragic combination of mechanical and human error. But it could change the world, allowing sub-orbital flight that would make even Concorde seem sluggish. Once the edge of the atmosphere is no longer a frontier, the cost and difficulty of maintaining satellites and launching more and more ambitious projects to explore our solar system will dwindle, while our horizons will expand. This won’t be the end of Virgin Galactic, but after almost ten years since its inception, our excitement and interest has waned, while our impatience and doubts only grow. More than any technical limitation or financial burden, this is the biggest threat to our heady goals.

This will probably always be the way with science and engineering at the forefront of human ability. What starts as bright-eyed ambition and exhilaration at the prospect of crossing some new frontier will eventually fester into doubts about the cost in relation to the supposed benefit. Sometimes there will be disasters, and these can strip away our confidence and faith in an instant. Naysaying can cause us to see failure as inevitability, and can belittle otherwise fantastic moments for human exploration, like the Rosetta mission.

We risk not only losing sight of the next step, but of why we wanted to get there in the first place. The cost of the Rosetta mission shouldn’t be sniffed at, but its success will lead to future successes, and its potential failure shouldn’t curtail the whole enterprise.

Today, it is harder to get into space than it was ten years ago. This is not because it is prohibitively expensive or riskier, but because our fear has paralysed us, and our interpretation of the benefits has dwindled. Hesitancy will only lead to slower progress. If we spent more time celebrating our achievements and ambitions and less time quibbling about their virtue and value, we would not only experience greater success, but would also perceive greater value in that success.

Had our attitude been different over the last half-century, it could well have been a person, not a probe, landing on that comet. A human who would have shown no hesitation in firing their harpoon, without fear of sharing Ahab’s fate.