“Here's the essence of risk management: Risk no more than you can afford to lose, and also risk enough so that a win is meaningful. If there is no such amount, don't play.”

Becoming Light: Poems New and Selected (1991)
Variant: ... if you don't risk anything, you risk even more.

Rich Dad Poor Dad: What the Rich Teach Their Kids About Money-That the Poor and the Middle Class Do Not!

Source: Uncle Tom's Cabin

Source: The Passion

Source: Raja-Yoga

Pt. 1, Ch. 2 - p.36
Giovanni's Room (1956)

From his book: Fault Lines: How Hidden Fractures Still Threaten the World Economy (2010) https://books.google.co.in/books/about/Fault_Lines.html?id=2RB3j_YfEg0C

Variant: You can't outwit fate by standing on the sidelines placing little side bets about the outcome of life. Either you wade in, risk everything you have to play the game or you don't play at all. And if you can't play, you can't win.
Source: Paradise

Frequently attributed to Nin, but without cited source in her work (possibly due to a quotation in Living on Purpose: Straight Answers to Universal Questions (2000) by Dan Millman that attributed the quote to Nin without source).
In March 2013, a former Director of Public Relations at John F. Kennedy University in Orinda, Elizabeth Appell, claimed she had authored the quote in 1979 for an inspirational header on a class schedule: http://anaisninblog.skybluepress.com/2013/03/who-wrote-risk-is-the-mystery-solved/
Disputed
Variant: The day came when the risk to remain tight in a bud was more painful than the risk it took to blossom.