We show that the global nature of trapped particle motion in phase space makes it entirely plausible that particles with pitch angles near 90 ¿ are trapped for extremely long times, probably indefinitely. The long observed lifetimes of trapped particles can immediately be accounted for by this former population. For particles with low pitch angles and 'overstability' develops which serves to produce rapid variations in pitch angle and, presumably, random walk into the loss cone. Numerical calculations are needed to assess how this transition to overstability depends on particle rigidity.