"When all of these factors are taken together it is not surprising that sprites have been so elusive. However, they can be seen with the unaided human eye." The area around us isn't very suitable for watching for them, but I'll have to try next time I'm out in open land. What you want is dark, dark-adjusted eyes, clear skies to a distant (200 mile) thunderstorm, and something (paper or whatever) to block out the dazzle from the bright lower lightening. Watch above the storm for faint flashes.
There are still lots of hidden and unexpected things not far away.