入木三分 [- - sān fēn](形容书法笔力强劲; 比喻见解、议论深刻) written in a forceful hand; having forceful strokes of ideas [views;observations];enter three-tenths of an inch into the timber — vigorous effort; keen; penetrating; profound:
•¶ 他的分析真是入木三分。 His analysis was really penetrating.