pí fú hàn dà shù
lit. an ant trying to shake a big tree (idiom)
fig. to overrate one's own strength; also written 蚍蜉撼樹|蚍蜉撼树[pi2 fu2 han4 shu4]
蚍
pí
used in 蚍蜉[pi2 fu2]
蜉
fú
撼
hàn
to shake
大
dà
big; large; great
树
shù
tree