Answer:
First , i think we should know the meaning
1) Regular change , e.g. day and night
2) Irregular change[use plural]
They remained friends in the vicissitudes of 40 years. [2]
God made two great lights . . . To illuminate the earth and rule the day In their vicissitude, and rule the night. --Milton [1]
Vicissitude occurs on my face when I forget to shave.
Day traders usually don't survive the vicissitude of the market place for long.