Google X, Google’s private research laboratory, puts billions of dollars into moonshot projects with long odds that have the potential to change the world. Ongoing examples include Google Glass, driverless cars, and glucose-monitoring contact lenses.

More important than how the lab comes up with ideas, is how it rejects and kills them. Potentially amazing projects like space elevators, hoverboards, and teleportation have been discarded or put on the back burner as the company seeks what writer Jon Gertner calls “the practical side of crazy” in a profile of the lab for Fast Company.

Here are a few of the key lessons from how the team at Google X thinks:

Rejecting ideas is as important as coming up with them

For an idea to even be considered, it has to make its way through the Google X Rapid Evaluation team. Their primary approach to ideas is to do everything humanly and technologically possible to make them fall apart. The team looks at possible scale, the impact of the fix, and potential technology risks.

“Will it really solve the problem? Can the thing actually be built? Then they ­consider the social risks. If we can build it, will it–can it–actually be used?” Gertner writes.

The idea is to think about these issues and work on them early rather than after years and billions have been invested. Glass, for example, has privacy issues. Driverless cars have legal problems. But those were seen as surmountable. If an idea passes those initial tests, the group will put together a quick prototype.

This process has killed potentially transformative technologies. Space elevators would have upended space travel. But the materials science just isn’t there to support a cable to space. And though the group had a promising early prototype for a hoverboard technology, the costs and complications weren’t justified by the potential social impact.

At one point the group talked about teleporting. Some insurmountable violations of the laws of physics came up. But discussions helped lead to useful insights into encrypted communications, according to Gertner.

Few projects get commissioned, and many get killed along the way. Even though Google X has a long leash, lots of money, and a mandate to go for the moon, it embraces the reality of failure.

“When we let it go, it’s a positive thing,” Rapid Evaluation team lead Rich DeVaul told Fast Company. “We’re saying, ‘This is great: Now we get to work on other things.'”

Don’t try to solve lame problems

To even be subjected to that onslaught of criticism, any potential X project has to meet a few criteria:

It must address a problem that affects millions (or billions) of people

The solution must be radical enough that it resembles, in part, science fiction

It must tap technology that is or is nearly unobtainable

No project can be incremental

That last principle comes from a philosophy that taking big risks is simply more practical.

“It’s so hard to do almost anything in this world,” DeVaul says. “Getting out of bed in the morning can be hard for me. But attacking a problem that is twice as big or 10 times as big is not twice or 10 times as hard.”

He argues that it’s easier to make progress on big problems instead of wringing the next 5% out of something. Building a car that gets 80 miles per gallon would be great but wouldn’t truly solve fundamental problems of fossil fuel use or emissions, DeVaul’s thinking goes.

Going for 500 miles per gallon not only addresses the problem, it forces you to come up with a real solution because there’s no way you can get that from existing automotive design. Trying to tackle that kind of problem ends up being more effective, even if it takes much longer.