Here's MY favorite explanation:
It's late on a dark and stormy night and you've been driving down a lonely road. You're stopped by the local police on a flimsy pretext. They ask if you've been drinking. You say no.
They ask you to get out of the car, walk a straight line, which you do; but you wobble a bit because you've been sitting in the car for hours.
So they ask you to close your eyes, put your arms straight out in front of you and touch your fingertips together. If you get it exactly right, you cannot dissolve. If you blow it and your fingers overlap one or two joints, that's the possible length of your transition.
Hoping this real-world example helps you on your next traffic stop, I am your
Uncle Grump