Am I trying to take someone's Frosted Flakes? Is this sage advice or an old wives' tale?
There's this from William Safire in The New York Times, writing about the phrase's origin:
'Ch'i 'hu nan hsia pei' goes the Chinese proverb, translated in 1875 as 'He who rides a tiger is afraid to dismount.' The Oxford Dictionary of Proverbs interprets the old Asian metaphor as 'Once a dangerous or troublesome venture is begun, the safest course is to carry it through to the end.'
This lends credence to the Chinese-origin theory.
There's a discussion regarding this one here.
There's a similar proverb: "He who rides a tiger is afraid to dismount - Once a dangerous or troublesome venture is begun, the safest course is to carry it through to the end. 1875 W. Scarborough 'Collection of Chinese Proverbs.'"
My inclination however is to disagree that "tiger by the tail" has the same meaning. In the proverb, getting off the tiger is dangerous (or fatal), and it's usually used when relinquishing control of something is difficult.
In the phrase in question, however, the tiger is certainly capable of causing harm and holding its tail is likely to enrage it. Thus, in practice, the phrase means, "trying to control X - or be in possession of X - is extremely dangerous."
Thus, at the Fukushima Nuclear Plant, the rescue crews are in danger because of the radiation, but the crisis will worsen if they flee; they have to stay in spite of the danger ("he who rides the tiger..."). However, the act of trying to control the reactors is deadly, and they have a tiger by the tail.
I feel "having a tiger by the tail" is best described as someone in a situation with a powerful beast foolishly taking a tiger by the tail thinking this is how you can catch it and control it. Basically underestimate your foe you will pay and pay dearly. For example. If someone hurt's a man's daughter. A normal sane man can turn into a rabid beast a gnaw your face off if need be. That's catching a tiger by its tail. The response to the act of hanging onto the tail will be with fangs and claws. Not restraint and control as you tried with him.
I remember reading this tale as a child:
Once a man was walking in the jungle and saw something move behind a tree and grabbed it. 'It' turned out to be the tail of a tiger that was resting on the other side of the tree. Startled the tiger, tried to run around the tree and encountered the man holding the end of its tail. As it tried to catch him, its tail yanked the man away from it. The man soon realized that he had made a terrible mistake but had no real choice. He held on to the tiger's tail as it chased him around the tree. — The End.
I have always believed the meaning to be that givin in the 1827 Journal quoted above - one who "has a tiger by the tail" is equally imperiled by holding it and releasing it. If held, the tiger can turn around and kill the person. If let loose, it can still kill the person. Catching a tiger by the tail is a naive and dangerous way to deal with the beast, and one who has one by the tail made an error in dealing with a troublesome situation.