As the sizes of (nano-)devices are aggressively scaled deep towards the nanometer range, the design and manufacturing of future (nano-)circuits will become extremely complex and inevitably introduce more defects, while their functioning will be adversely affected by (transient) faults. Therefore, accurately calculating the reliability of future designs will become a very important factor for (nano-)circuit designers as they investigate several alternatives for optimizing the trade-offs between the conflicting metrics of area-power-energy-delay versus reliability. This paper studies the effect of the input vectors on the (nano-)circuit's reliability, and introduces a time-efficient method for quickly and accurately identifying the lower/upper reliability bounds. Simulations results support the claim that the absolute difference between the lowest and the highest achievable reliability is of one-to-two orders of magnitude. Therefore, future designs should consider the worst case input vector(s) in order to guarantee the required reliability margins.