The answer to this classic riddle is a hole. Every time you take material away from a hole, whether you’re digging in the ground, drilling through wood, or carving into stone, the hole itself gets larger. It’s a satisfying bit of wordplay: you’re not adding anything, yet the “thing” grows precisely because of what you remove.
But the riddle works so well because it touches on a real physical principle. Holes, voids, and gaps show up everywhere in science and daily life, and many of them genuinely do expand the more you take away. Here’s how that concept plays out in ways you might not expect.
Why Digging Makes a Bigger Hole Than You Think
When engineers calculate how much earth needs to move for a road or foundation, they deal with a quirk called swell. One cubic yard of undisturbed soil doesn’t stay one cubic yard once you scoop it out. That same dirt can expand to about 1.25 cubic yards in the back of a truck because it’s no longer packed tightly together. So the hole you’ve created is one size, the pile of dirt beside it looks even bigger, and if you tried to compact all that soil back into the hole, it would only fill about 65 to 85 percent of the original space.
This means that once you start digging, the void you’ve made is effectively permanent. You can’t perfectly undo it. The Federal Highway Administration uses a straightforward formula to calculate excavation volumes: multiply the average of two cross-sectional areas by the distance between them. It’s simple math for a concept the riddle captures intuitively. Taking from the ground makes the empty space grow, and the material you removed won’t neatly fill it back in.
Sleep Debt: The Gap That Grows Nightly
Sleep is another thing where every bit you “take away” makes the deficit bigger, and the consequences stack up in a surprisingly linear fashion. In one of the most detailed sleep restriction experiments conducted, researchers tracked people limited to four, six, or eight hours in bed each night for two weeks. Those who got eight hours showed no cognitive decline at all. But the groups restricted to four or six hours got steadily worse, day after day, in a nearly straight-line pattern.
After two weeks of sleeping just six hours a night, participants performed as poorly on attention and memory tests as someone who had stayed awake for an entire night. Those restricted to four hours were as impaired as someone awake for two full nights straight. The critical threshold for avoiding any accumulation of sleep debt appears to be right around 8.16 hours of actual sleep. Anything less, and the void grows a little wider each night. What makes this particularly dangerous is that people consistently underestimate how impaired they’ve become. The hole gets bigger, but you lose the ability to see its edges.
How Bones Develop Invisible Gaps
Your skeleton is constantly being remodeled. Specialized cells break down old bone while others build new tissue in its place. When more gets taken away than rebuilt, the internal structure of bone develops wider and wider gaps. This is the core of osteoporosis, and researchers can now measure exactly how those spaces grow.
A 2025 study examining jawbone in pre- and postmenopausal women found that the spacing between tiny bone struts (the scaffold-like internal architecture) increased significantly after menopause. In one region, the average gap between struts went from 0.60 mm to 0.84 mm. In another area, it jumped from 0.91 mm to 1.58 mm, nearly doubling. At the same time, the overall volume of bone tissue dropped from about 33 percent of total volume to under 18 percent. Every bit of mineral the body takes away and fails to replace makes the internal voids larger, and the bone weaker.
The Pleasure Void in Addiction
The riddle’s logic applies to brain chemistry in a way that helps explain why addiction is so difficult to overcome. Your brain’s reward system relies on a chemical signaling process that produces feelings of pleasure and motivation. When a substance like an opioid floods that system, the brain compensates by dialing down its own capacity to feel good. It’s as if the brain is trying to restore balance, but the result is a growing emotional void.
Chronic opioid use triggers the activation of a separate receptor system that produces the opposite of pleasure: anxiety and a low, flat mood. At the same time, the brain’s normal feel-good signaling becomes sluggish. Researchers describe this as “dopaminergic hypofunction,” but the experience is simpler to understand. Each time a person uses, the brain removes a little more of its natural reward capacity. The gap between how they feel sober and how they felt before they ever used the substance gets wider. This negative emotional state becomes its own powerful driver of continued use, because the drug temporarily fills the very hole it created.
Wounds That Tunnel Deeper
Pressure ulcers, sometimes called bedsores, are a literal version of the riddle in medical form. They begin as surface damage but can progress into deep voids in tissue. Clinicians classify them in stages. At Stage III, full-thickness tissue has been lost, and the wound may include tunneling, where the damage extends sideways under intact skin. At Stage IV, the void has grown to expose bone, tendon, or muscle, often with extensive tunneling and undermining of surrounding tissue.
Each bit of tissue that dies and sloughs away makes the wound larger. The body is losing material, and the cavity expands. Measurement involves tracking length, width, and depth over time, along with mapping any tunnels that branch off from the main wound. Without intervention, these wounds follow the riddle’s logic perfectly: the more tissue is lost, the bigger the void becomes.
Even Teeth Follow the Pattern
Tooth decay is another process where removal of material creates a growing space. Acids produced by bacteria dissolve minerals from the tooth’s enamel surface, creating microscopic voids that gradually merge and deepen. The progression from an enamel-only lesion to one that reaches the softer layer underneath takes a relatively long period, often requiring at least three years of observation in clinical studies to reliably measure. Once past the enamel, though, the softer interior erodes more quickly. A lesion under 5 mm is classified as an erosion. Once it crosses that threshold, it’s officially an ulcer or cavity, a hole that will only keep growing without treatment.
The riddle’s answer is simple, but the principle behind it runs deep. Holes, gaps, debts, and voids across physics, biology, and neuroscience all share the same counterintuitive property: they are defined by absence, and they grow through subtraction. Every time you take from them, they get bigger.