Chinese Idiom -- 虎头蛇尾

虎(hǔ)头(tóu)蛇(shé)尾(wěi) 

It literally means “tiger head” and “snake tail”. "tiger head" is strong and powerful; while "snake tail" is tiny and weak. In English, it means someone who enters an a whirlwind but depart as an ant. 

Example: 我(wǒ)的(de)新(xīn)年(nián)计(jì)划(huà)是(shì)学(xué)中(zhōng)文(wén)。我(wǒ)要(yào)坚(jiān)持(chí)，不(bù)能(néng)虎(hǔ)头(tóu)蛇(shé)尾(wěi)。