quit＝to free（使自由）,to release（免除）
n (often derog 常作贬义) person who does not finish a task he has started, esp one that is done as a duty 对工作半途而废的人; （尤指对职责）不善始善终的人
*I've asked you to do this for me because I know you're not a quitter. 我要求你为我做这件事, 因为我知道你做事不虎头蛇尾.
informal someone who does not have the determination or courage to finish something that is difficult