苦练

苦练	kǔ liàn	to train hard / to practice diligently / hard work / blood, sweat, and tears
苦	kǔ	bitter / hardship / pain / to suffer / to bring suffering to / painstakingly
练	liàn	to practice / to train / to drill / to perfect (one's skill) / exercise / (literary) white silk / to boil and scour raw silk