Classic Fly casting instruction states that tailing loops have a lot of causes. However, actually there are only two causes for a tail:
1.- An acceleration that the caster doesn't keep during the whole stroke, i.e., he slows down before reaching the end of the stroke.
2.- A casting angle too small to match the bend in the rod.
Both make the tip of the rod sharply deviate from the ideal straight line path, thus creating a transverse wave that travels along the line (as seen here:

Starting the casting stroke too soon has been regarded as a cause of tailing loops. It can be for sure, but for it to be there must be something more.
As this clip shows, a serious timing fault doesn't cause a tail by itself. For the tail to appear the caster should have made an abrupt application of force at any point along the stroke, or the casting angle should be so small that even a progressive application of force would make the rod tip to dip, and rise, crossing the ideal Straight Line Path. It doesn't happens either.

So saying that bad timing is a cause of tailing loops is a gross generalization; since all tailing loops are exclusively related to force application and casting angle, bad timing can produce tails... or not.

More footage on the same issue:

Loading more stuff…

Hmm…it looks like things are taking a while to load. Try again?

Loading videos…