  Tremendous efforts are required to scale the summit of observing neutrinoless
double beta decay ($0 \nu \beta \beta$). This article quantitatively explores
the interplay between exposure (target mass X data taking time) and background
levels in $0 \nu \beta \beta$ experiments. In particular, background reduction
can substantially alleviate the necessity of unrealistic large exposure as the
normal mass hierarchy (NH) is probed. The non-degenerate (ND)-NH can be covered
with an exposure of O(100) ton-year, which is only an order of magnitude larger
than those planned for next generation projects - provided that the background
could be reduced by 0($10^{-6}$) relative to the current best levels. It
follows that background suppression will be playing increasingly important and
investment-effective, if not determining, roles in future $0 \nu \beta \beta$
experiments with sensitivity goals of approaching and covering ND-NH.
