All fuzzy inside

Sometimes, a whole lot of times, things aren't as simple as black and white. Sometimes they are thrown together and blended into an unintelligible mess. If you have to deal with such a mess, then strict, boolean logic-based rules and algorithms will only make your mess bigger (and maybe some segfaults).
Sometimes you need to estimate a state, to respond proportionally, or to reason under uncertainty. In those cases, you must use a probabilistic interpretation instead of a brittle, hardcoded case-based controller.
Maybe the simplest and most robust system that deals with this is fuzzy logic.

Shamelessly stolen from Wikipedia

As you might see in the graph, the temperature is a continuous variable, while a system has 3 discrete responses: cold, warm, or hot. This could be, for instance, a thermostat being able to cool or heat up a room.

Some of its robustness lies in being able to transition from one state to another in a smooth way, without starting and stopping abruptly at the border between them. Also, the gradient of the responses may be adjusted, to compensate for whatever subjectivity there may be in deciding the thresholds, or for whatever errors there may be in the measurement, since the real world can be very noisy.

There also exist more advanced controllers similar to this, such as the PID controller, which also takes into account the integral and the derivative of the signal with respect to time. However, in order to decide how much importance is assigned to each component (the proportional, integral, and derivative responses), extra parameters are required, which reduces the basin of initial conditions which will lead to a "good" solution. The more parameters that need tuning, the more unstable a system is.

This is loosely similar to the principle of Occam's razor - the fewer assumptions an explanation requires, the more likely it is to be correct. Also, this is why laziness is one of the programmers' virtues - generally, the simpler the code, the better it is (given that it performs the required job).