vicissitudes, the way that the world or a person prospers one day and declines the next

一栄一落: vicissitudes

You should treasure every encounter, for it will never recur.

dotting the i's and crossing the t's

successive series of questions and responses

zero

a custom, usual practice, habit / a precedent / the aforementioned / a case, an instance, an illustration, an example

a bow, the gesture of bending at the waist / an expression of thanks or gratitude

age

miracle drug