  We discuss the nonlinear origin of the power-law tail in the long-time
evolution of a spherically symmetric self-gravitating massless scalar field in
even-dimensional spacetimes. Using third-order perturbation method, we derive
explicit expressions for the tail (the decay rate and the amplitude) for
solutions starting from small initial data and we verify this prediction via
numerical integration of the Einstein-scalar field equations in four and six
dimensions. Our results show that the coincidence of decay rates of linear and
nonlinear tails in four dimensions (which has misguided some tail hunters in
the past) is in a sense accidental and does not hold in higher dimensions.
