yang jian was the regent（摄政王） of the last king of northern zhou(557-581). his wife advised him: "northern zhou is dying. now it is as if you are riding on the back of a tiger. it will be *erous to dismount（下马，下车） . you can do nothing but continue." yang jian thought this quite reasonable. later, he founded the sui dynasty, and united china once *.
this idom is used as a metaphor1 meaning that one is in a difficult situation and cannot * but ontinue to pursue one's sourse.
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