And why some things get invented and some don't.
My own example: the wheel was invented 5,500 years ago; it took us 5,480 years to figure out we could put them on suitcases.
Or some crimes get discovered and some don't. The Yorkshire Ripper, for eg:
New ideas are especially fragile because they usually take hold in one, often fairly random person who spots something tangential that nobody else thinks important.
DC Andy Laptew, the first person to put Peter Sutcliffe in the frame as the Yorkshire Ripper, was another case in point. His suspicions started with a chance observation. He and his partner always told the same ice–breaking joke when interviewing a couple: 'Now's the chance to get rid of your husband.' His visit to Sutcliffe was the first time no one laughed or reacted. He then noticed Sutcliffe had a gap in his teeth matching dental evidence from the crimes.
