  First passage time plays a fundamental role in dynamical characterization of
stochastic processes. Crucially, our current understanding on the problem is
almost entirely relies on the theoretical formulations, which assume the
processes under consideration are Markovian, despite abundant non-Markovian
dynamics found in complex systems. Here we introduce a simple and physically
appealing analytical framework to calculate the first passage time statistics
of non-Markovian walkers grounded in a fundamental principle of nonequilibrium
statistical physics that connects the fluctuations in stochastic system to the
macroscopic law of relaxation. Pinpointing a crucial role of the memory in the
first passage time statistics, our approach not only allows us to confirm the
non-trivial scaling conjectures for fractional Brownian motion, but also
provides a formula of the first passage time distribution in the entire time
scale, and establish the quantitative description of the position probability
distribution of non-Markovian walkers in the presence of absorbing boundary.
