  Measurements of any property of a microscopic system are bound to show
significant deviations from the average, due to thermal fluctuations. For
time-integrated currents such as heat, work or entropy production in a steady
state, it is in fact known that there will be long stretches of fluctuations
both above as well as below the average, occurring equally likely at large
times. In this paper we show that for any finite-time measurement in a
non-equilibrium steady state - rather counter-intuitively - fluctuations below
the average are more probable. This discrepancy is higher when the system is
further away from equilibrium. For overdamped diffusive processes, there is
even an optimal time when time-integrated current fluctuations mostly lie below
the average. We demonstrate that these effects result from the non-monotonic
skewness of current fluctuations and provide evidence that they are easily
observable in experiments. We also discuss their extensions to discrete space
Markov jump processes and implications to biological and synthetic microscopic
engines.
