  Analog quantum simulators (AQS) will likely be the first nontrivial
application of quantum technology for predictive simulation. However, there
remain questions regarding the degree of confidence that can be placed in the
results of AQS since they do not naturally incorporate error correction.
Specifically, how do we know whether an analog simulation of a quantum model
will produce predictions that agree with the ideal model in the presence of
inevitable imperfections? At the same time, there is a widely held expectation
that certain quantum simulation questions will be robust to errors and
perturbations in the underlying hardware. Resolving these two points of view is
a critical step in making the most of this promising technology. In this work
we formalize the notion of AQS reliability by determining sensitivity of AQS
outputs to underlying parameters, and formulate conditions for robust
simulation. Our approach naturally reveals the importance of model symmetries
in dictating the robust properties. To demonstrate the approach, we
characterize the robust features of a variety of quantum many-body models.
