“The only thing between you and your dreams is your beliefs.”

Source: Notes On A Scandal

Source: Blood Promise

Variant: The only thing that stands between you and your well-being is a simple fact: you have allowed your thoughts and emotions to take instruction from the outside rather than the inside. On
Source: Inner Engineering: A Yogi's Guide to Joy

Jordan Belfort played by Leonardo DiCaprio in The Wolf of Wall Street (2013)

Source: Julie and Julia: 365 Days, 524 Recipes, 1 Tiny Apartment Kitchen: How One Girl Risked Her Marriage, Her Job, and Her Sanity to Master the Art of Living

As quoted in "New Hampshire Town Reeling From Shock, Grief" by Bob Drogin in The Los Angeles Times (30 Januray 1986)

Source: Vanishing Acts

Source: Meditations

This has sometimes been paraphrased: "The simple things are also the most extraordinary things, and only the wise can see them."
Source: The Alchemist (1988), p. 15.