Heroes are often admired for their ability to act without having “one thought too many,” as Bernard Williams put it. Likewise, the unhesitating decisions of masterful athletes and artists are part of their fascination. Examples like these make clear that spontaneity can represent an ideal. However, recent literature in empirical psychology has shown how vulnerable our spontaneous inclinations can be to bias, shortsightedness, and irrationality. How can we make sense of these different roles that spontaneity plays in our lives? This chapter describes several case studies of both the “virtues” and “vices” of spontaneity. It lays out the arguments to come in the book in support of the claim that understanding both the virtues and vices of spontaneity requires understanding the implicit mind. The concept of “implicitness” is itself discussed, and a roadmap for the book is provided.