Risk "Reject"

As a project manager, one of the most important things you’ll have to analyze is risk.

Elaborate more on what it means to "reject" risk.   This part I need 4 quality references from the web www.xxx.com....... Current 2015-2018!

Separate out these two parts not a paper just informational gathering on the topic.

Also:  in  a separate part with its own references

Secondary risks and what causes them........ This part I need 5 quality references from the web www.xxx.com  Current 2015-2018!