Correct

马失前蹄

/ mǎ shī qián tí / 
Strokes

Definition

lit. the horse loses its front hooves/fig. sudden failure through miscalculation or inattentiveness

Example

Definition

the horse stumbles; the horse trips (and falls on his knees)—make a mistake by accident; have an accidental setback

1
Cǐrén
此人
yībèizi
一辈子
zuòshì
做事
xiǎoxīnjǐnshèn
小心谨慎
  
,
dàn
但
yě
也
yǒu
有
mǎshīqiántí
马失前蹄
de
的
shíhou
时候
  
。

This man has been cautious all his life, but he's nonetheless slipped occasionally.