You have three boxes. One contains apples, one oranges and one both. All are labeled, and each label is wrong. Taking only one piece of fruit from only one box, how can you correctly label them all?

How do you weigh an elephant without using a scale?

What would you charge to wash all the windows in Manhattan?

If you were shrunk to the size of a pencil and put in a blender, how would you escape?

How would you market ping pong balls if ping pong were obsolete?

Don’t worry, there’s no need to explain why you’ve decided to enter the window washing business or for what highly personal reason you’ve taken up pachyderm measuring. There won’t be a test at the end of this article.

In fact, these are a few examples of famously hard questions asked by interviewers at some of America’s top companies, including Goldman Sachs, IBM and Microsoft, and they’re just the tip of the iceberg. Several years ago Seattle career coach Lewis Lin put together a list of 140 of the most dastardly questions asked over at Google, some of which make “name your greatest weakness” look positively slow-pitch. 

And yet, getting one of these stumpers at your next job interview may not necessarily be a deal breaker. Anything but, in fact, since it turns out that those mind bending questions actually make everyone happier… just, not during the interview itself.

A new study out from Glassdoor finds that more difficult job interviews, as reviewed by the candidates themselves, lead directly to greater employee satisfaction down the road. Employees are actually happier once they start working at places that put them through the wringer.

On a scale of one to five, hiring processes produce the best results at a “four,” or almost the hardest they can get.

After that, though, the doozy-slingers just seem to be trying to impress themselves. At a difficulty of five out of five happiness declines, proving that that guy who challenged you to interview yourself probably really was just being smug.

The connection, according to chief economist for Glassdoor Andrew Chamberlain, has to do with how well tailored an interview is at pulling out someone who’s right for a position. Hard questions might be tough medicine, but they can also better predict how someone will do when faced with real challenges.

Think about it like a dating process, he said. “They [the employer and employee] are both testing each other to see whether it would be a good fit," Chamberlain said. "They’re saying, 'Actually show me, right now, that you can do the job we’re hiring for.'”

Even more interestingly, this isn’t a cultural phenomenon. The results held up across six different countries, meaning that even the French prefer a real challenge when it comes to getting the job. 

Of course brain teasers aren’t the only way to suss out whether a candidate can prove his mettle. Interviewers use a wide variety of approaches, and these days the brain teaser is increasingly giving way to real-world challenges. Applicants might be handed a snippet of code or a hypothetical scenario and asked to generate a real-life solution.

After all, the best way to see if someone can do the job is, well, by asking him to do it.

Take it not only as a compliment but as a really good sign. When an employer wants to know, really know, that you can do the job, it sends two clear messages: you’ll likely work with effective colleagues, and you’re unlikely to get too far in over your own head.

It’s what makes a simplistic interview process an even greater red flag than one that’s too hard.

“From the candidate’s viewpoint,” Chamberlain said, “the big takeaway here is you should be worried if your interview was too easy, not too difficult. If you come away from an interview and you feel like it was too simple, there’s a chance that you’re not being well matched for the job.”

“Job interviews are the front line defense for company culture," he added. "It’s the gateway through which all employees come, and if it does a poor job of matching people up with positions it has an effect on company culture for years to come.”

The ripple effect of relaxing too much, or setting standards meaninglessly high, can spread all throughout a company’s structure, especially if a poor fit finds himself promoted into hiring authority.

So the moral of this story? Dive into those twisty, challenging, maddening and infuriating questions with gusto and resist the urge to commit violence with desk tchotchkes. It’s all for the best.

Oh, and for those curious about the answers to the questions above:

1. Select from the box labelled “Apples and Oranges.” Let’s say you pick an apple. Since the label is wrong, this box must be “Apples.” There are two boxes left, so swap the “Oranges” label onto the box previously marked “Apples;” that label has to move and there’s only one box it can go to. Put the “Apples” label onto the remaining box.

2. There are a few different answers to this question, but I prefer accelerating the poor elephant to 60 miles per hour in a vacuum, say high Earth orbit, and measuring the thrust. Using Newton (force = mass times acceleration), we can divide that thrust by that 60 mph to get the elephant’s mass.

Well, the former elephant. We did launch it into space after all.

Multiply by gravity to get weight. Do not submerge your elephant in a tank of water unless you already know its density, by which point your relationship with the animal has progressed from experimental to profoundly disturbing.

3. Street level or top floor? Probably about $8.00 an hour on the ground floor, more if I have to buy special equipment and insurance. Double that to have the elephant do it.

4. Depends. If our Bond villain forgot to account for density, just tap on the side of the glass and watch it shatter. Then find the un-shrinking device before that candy bar from lunch starts a cascade reaction. Otherwise there aren’t a lot of good answers to this one. You could use the blade to pry open your cell phone, then discharge the battery into the metal shaft to try and short out the motor. Or you could use that phone to just call Moneypenny for help.

5. Did you know that Lysol was once a surgical disinfectant? That coffee breaks were invented specifically to get people drinking coffee? That we take two Alka-Seltzer for no other reason than that the slogan says “plop plop, fizz fizz”? That most bottled water is poured from the tap?

A good ad can sell literally anything. Personally, for this, I’d go with household utility. From makeshift bottle caps to crafts and packing peanuts, a bag of ping pong balls can do anything. “Any chore, they’re not a bore! Not just for fun, grab one and done!”

Want to sell an obsolete product? Just stick it next to the PBR out in Brooklyn.