WoW: 冰凍三尺, 非一日之寒!

冰凍三尺   非一日之寒

bīng dòng sān chǐ , fēi yī rì zhī hán

Literally: A single day of sub-zero temperature is not enough to create three feet of ice.

Moral: Great things cannot be accomplished in a short period of time.

Source: Wikiquote