卖犊买刀 Sell the calf, buy a sword
Explanation
比喻不惜一切代价，准备战斗或从事某种事业。
The idiom refers to someone who spares no expense in preparing for a battle or undertaking.
Origin Story
话说战国时期，有个名叫李实的农夫，家境贫寒，只靠耕田为生。他养了一头健壮的耕牛，是家中主要的经济来源。然而，秦国大军压境，战火一触即发，李实心怀家国，毅然决定参军保卫家园。他知道，战场残酷，需要强大的实力才能保家卫国，于是他忍痛割爱，卖掉了心爱的耕牛，换来了锋利的武器，准备投身沙场，与强敌对抗。李实的故事在乡里传为佳话，后人用“卖犊买刀”来比喻为了国家或正义事业，不惜一切代价，贡献出自己的一切。
In the Warring States period, there was a poor farmer named Li Shi who made a living by farming. His most valuable possession was a strong ox. However, the Qin army was approaching, and war was imminent. Li Shi, with a patriotic heart, resolutely decided to join the army to defend his homeland. He knew that the battlefield was cruel and that he needed strength to protect his country. So, he painfully sold his beloved ox to buy sharp weapons and prepare to join the battlefield to fight against powerful enemies. Li Shi's story became a legend in his village, and later generations used "mài dú mǎi dāo" to describe someone who sacrifices everything for their country or a just cause.
Usage
多用于战争、战斗等场景，形容为了某种目的，不惜代价，舍弃一切。
It's often used in the context of war and battle, to describe someone who sacrifices everything to achieve a goal.
Examples
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他为了这次考试，真是卖犊买刀，放弃了所有娱乐活动，全力以赴。
ta wei le zhe ci kaoshi,zhen shi mai du mai dao,fangqi le suoyou yule huodong,quanli yifu
He really went all out for this exam; he sold the farm to buy a sword, giving up all recreational activities.