have a tiger by the tail 骑虎难下

这个短语的字面意思是：抓住老虎的尾巴。这是非常危险的局面，如果松开手，肯定对付不了凶猛的老虎。但是抓住老虎尾巴不放，看来也是凶多吉少，因为实际上本来也没有任何制服老虎的可能。中文所说的“骑虎难下”其实同这个短语的意思非常接近。

Once you start using heroin, you'll have a tiger by the tail. If you get hooked, you'll need more and more, it'll cost you more money, and you might have to steal to support the habit.

你一旦开始用海洛因，就很难找到退路。上瘾之后，需要量越来越大，需要更多的钱，甚至还要为了满足毒瘾去偷窃

毒品是老虎尾巴，说话不算话也可以是老虎尾巴。乔治•布什在竞选美国总统成功以后就有这样的教训。他1988年竞选的时候许诺说，当选后绝不增加征收联邦税。但是他登上总统宝座之后怎么样了呢？

He found he had a tiger by the tail. Despite his promise he had to raise taxes to cope with the deficit. And this helped Bill Clinton beat him in his try for re-election in 1992.

布什打破自己的许诺，增加征税，结果最终在连任竞选中被克林顿击败。

也许老虎尾巴还是不抓为好。