Algorithms

Search a sorted array by repeatedly dividing the search interval in half. Begin with an interval covering the whole array. If the value of the search key is less than the item in the middle of the interval, narrow the interval to the lower half. Otherwise narrow it to the upper half. Repeatedly check until the value is found or the interval is empty.

Especially if you're a coder, but does come up in real life too. Algorithms are underrated and probably underused - it comes up maybe 1% of the time, but in that 1% of the time, it's 100% important. These are real algorithms, with real-world application, but the lesson is in the paradigm..