The problem of sequentially determining the next, future, outcome of a specific binary individual sequence, based on its observed past, using a finite state (FS), predictor is considered. We define the finite state predictability of the (infinite) sequence x1... xn..., as the minimum fraction of prediction errors that can be made by any FS predictor and prove that this fraction of errors can be achieved, upto an arbitrary small prescribed distance, for each individual sequence, by fully sequential guessing schemes. The rate at which the sequential guessing schemes approach the predictability is also calculated. Furthermore, we provide an efficient guessing procedure, based on the incremental parsing algorithm used in the Lempel-Ziv data compression method, and show that its fraction of errors also approaches the predictability of the sequence. Finally we discuss some relations between compressibility and predictability, and suggest to use the predictability as an additional measure for the complexity, or randomness, of the sequence.