“I hope you step on a Lego” is such an apt curse that it has become a meme. Pages upon pages of YouTube videos detail the experience’s excruciating agony.

The comedian Steve Ranazzissi perhaps described the moment the best: “Last week I stepped on a Lego with my bare foot and I almost murdered my whole family.”

But why are the Lego blocks your 4-year-old leaves strewn around such nuggets of hell under the soles of your feet? And how does she manage to trip through them herself and continue on her merry way unscathed? Well, science has the answer.

There are a few factors that come together to make this such a painful experience, wrote Karl Smallwood of Today I Found Out (via Yahoo). First of all, the sole of the foot is highly sensitive to pain (and tickling), because of the many nerve endings there that convey information and help keep the body balanced.

And those plastic blocks are designed to be pretty astonishingly hard, with sharp corners to boot. You could apply 950 lbs, or stack 375,000 lego bricks, before one would crack. That means that as your foot stomps down on a block, the plastic doesn’t crack or crumble, its tiny evil ridges remaining intact as they dig into the ball of your foot.

The sharp corners also exacerbate the pain, New York University physics professor Tycho Sleator tells Quartz via email. Pressure is equal to the amount of force divided by the area to which that force is applied, he explains. “When you step on something with a sharp corner, the force from the corner is concentrated over a very small region of your foot. This would result in a very high pressure on that small region of your foot.”

That also means that Lego encounters probably hurt you more than they do your lighter-weight kid, because the surface of the Lego matches the amount of pressure bearing down on it. When walking, that isn’t just the pressure of gravity: Movement multiplies your standing weight. For example, you might be exerting pressure of up to twice your body weight with each step just by walking, and running produces pressure of up to nine times your weight.

And of course, there’s the ubiquity of Lego bricks, which parents know tend to lurk in the shadows of play areas around the world. The company points out that, laid end to end, 45.7 billion Lego bricks sold in 2012 alone would stretch around Earth more than 18 times.

Legos don’t seem to be disappearing any time soon—the company’s net profit increased by 15% last year, compared to the year before. But there is one way of averting this menace: Just store your Legos right in the first place.