When doing things, you should see them through from start to finish - you can't give up halfway.
Tips
history
From 《庄子·大宗师》 (Warring States): 善妖善老,善始善终 - 'good in youth and in age, good at the start and at the end.' Also cited in Sima Qian's 《史记·陈丞相世家赞》 praising Chen Ping's whole career as 善始善终.
usage
Natural pairing with 半途而废 ('to give up halfway') as its opposite.