A useful way to hold this word: faint means weak, and -hearted points at the heart you act with. So the picture is a person whose heart is not fully in it — they start the job, meet the first push-back, and stop. Everything the word does comes from that one moment of stopping early.
One branch
心力很弱的動作與人
一個是直接描述那個太早停下來的人或動作；另一個把「那群會太早停下來的人」整批拿來當門檻。
adjective · C1
Done without much force or courage, because the person does not really want to do it or does not believe it will work. It can also describe a person who loses their nerve as soon as something looks hard.
不夠起勁、膽怯的