1 It means that a person will experience countless ups and downs in his life, and sometimes he will be lucky and sometimes unlucky, so he uses the metaphor of getting on and off.

2 Or it can be said that in love, someone will follow you. Walking by, you may not know which car you will get into, or you may get off and change to another car, but in the end you will find the one you are most satisfied with

Personal opinion, hope to adopt it