yī bǐ bù gǒu
lit. not even one stroke is negligent (idiom)
fig. to write characters (calligraphy) in which every stroke is placed perfectly
一
yī
one
笔
bǐ
writing brush; writing implement (pen, pencil etc) (CL:支[zhi1],枝[zhi1])
不
bù
no; not so
苟
gǒu
(literary) if indeed