Before Wilbur and Orville Wright, no one but mythical characters flew. Flying machines that had been invented didn't work properly because they could not be controlled in flight. Even the Wright brothers had a seven-year struggle. (This link takes you to a crash of their 1900 glider.) Things we take for granted today - how to use lift, thrust, weight and drag to fly - were uncommon concepts before the Wright brothers.
After the Wright brothers, the world changed. Darrel Collins, from Kitty Hawk National Historical Park, said it best:
Before the Wright Brothers, no one in aviation did anything fundamentally right. Since the Wright Brothers, no one has done anything fundamentally different.
From watching birds fly, the Wright brothers knew a bird rolls right or left when it changes the angle where the wind meets its wings. The change in angle causes one wing to tilt up while the other wing simultaneously tilts down. No one had figured out how to translate what a bird can do naturally into what a plane could do mechanically.
Wilbur and Orville owned a bike shop in Dayton, Ohio. It was the very things they knew, and did, as bike-shop owners which helped them figure out what no one before them had fully understood. While helping a bike shop customer in 1899, Will discovered a major breakthrough: How to create, for a flying machine, a bird’s ability to execute a balanced, coordinated turn.
Puzzling how to make a piece of machinery work like a bird’s wing, Will fiddled with the packaging box of an inner tube he had just sold to his customer. When he squeezed opposite diagonal corners of the box, it twisted.
It occurred to Will that the top and bottom of the box were just like the wings of a biplane. If he used cables to draw the spars and struts of a biplane's wings together, he could do to flying machines what he had done to the box. And - if it worked as he imagined - he would warp the wings so one side tilted down while the other side tilted up. The side that was tilted down would give the biplane more lift, thereby enabling him to roll it right or left - imitating birds in flight.
Wilbur had come upon the first of many Wright discoveries. "Wing warping" (or, the aileron principle of flight) gave the Wright brothers a way to properly control one significant aspect of a biplane's movement.
Armed with their discovery, the brothers made gliders. In 1901 they took one to Kitty Hawk, North Carolina. They figured the wind along the seashore would help them get more lift as they launched their glider, while the sand would provide a soft-landing if they crashed. During their trials, they flew their gliders more than 700 times.
While their glider was impressive, as were their flights, they still had to solve the main problem. How would they create and control a heavier-than-air, engine-powered machine that could take off, fly and land safely? Just being able to tilt the wings, so the plane could properly roll, was not enough. The glider flights had not produced the kind of lift the brothers expected.
Wilbur was discouraged. He told Orville man would not fly for another thousand years. He was off by 999.