  The weak value, introduced by Aharonov et al. to extend the conventional
scope of physical observables in quantum mechanics, is an intriguing concept
which sheds new light on quantum foundations and is also useful for precision
measurement, but it poses serious questions on its physical meaning due to the
unconventional features including the complexity of its value. In this paper we
point out that the weak value has a direct connection with the wave-particle
duality, in the sense that the wave nature manifests itself in the imaginary
part while the particle nature in the real part. This is illustrated by the
double slit experiment, where we argue, with no conflict with complementarity,
that the trajectory of the particle can be inferred based on the weak value
without destroying the interference.
