Whenever you see the word "aviation," you don't want to see the words "lawn dart" immediately afterwards. They just shouldn't be linked. And yet, due to a quirk of the human brain, they are. The Lawn Dart Effect is the ultimate example of why you shouldn't trust your gut — especially when flying.
Early planes were homemade contraptions of wood and metal with a motor inside. They were meant mostly for thrill riders, and those thrill riders navigated in clear weather and with the ground in sight. As a result, most riders believed that they had a feeling for the navigation of the plane. They didn't. When pilots flew at night, or into clouds, it wasn't unusual for them to come out flying at a completely different angle than they imagined, or sometimes entirely upside down.
Some say it was the loss of the sight of the Earth, but it was actually a combination of two factors. Of course, we partly navigate by using the data from our eyes to make sure we're on a clear course. But we also navigate by the feel of the Earth pulling us straight down. Rarely in our evolution did we get the chance to experience more than one g of acceleration that might come from somewhere other than the ground. When they could see, the pilots made up for the loss of a clear sense of gravity. When they couldn't, things got bad.
Close your eyes and tilt your head up. How do you know where the ground is? Ah, yes, it's the thing that's pulling your head backwards. If you scoot down on your chair, you can lean your head on the back. Now your head is being supported, but the pressure of that support, directly behind your head, lets you know that it's tilted upwards. Now imagine you are a pilot, and the ground is nowhere in sight. You're keeping your plane steady, but you're going to speed it up a notch. As you speed up, you suddenly feel your head get pushed back against the seat behind you.
This is what you'd expect. As the plane accelerates, it puts pressure on your head (and body) to push you forward. But that's not what a lifetime of experience makes you believe. When there's a mysterious force pulling your head back against the seat behind you, it must be gravity. You must be going up. You tilt the plane back down to compensate. The next thing you know, the ground is rushing up at you.
The Lawn Dart Effect was given its gruesome name because pilots, when accelerating, would sometimes seem to steer right down into the ground. The path of the plane reminded observers of a lawn dart. The acceleration would cause the pilots to feel that they were tilted upwards, when they were actually flying level. They'd steer downwards to compensate. This is one of the reasons why navigational equipment is so crucial. Instincts, sadly, are easier to confuse.