苦心

painstaking effort / to take a lot of trouble / laborious at pains

bitter / hardship / pain / to suffer / to bring suffering to / painstakingly

heart / mind / intention / center / core / CL:顆|颗[ke1],個|个[ge4]

to take a lot of trouble (idiom); painstaking / at the cost of a lot of effort

to build up an enterprise through painstaking efforts

to make painstaking efforts (idiom); after much trouble / to work hard at sth

Heaven will not disappoint the person who tries (idiom). If you try hard, you're bound to succeed eventually.