In contrast with exact algorithms whose worst-case time complexity is known (see Chapter 1), metaheuristics do not provide that kind of bound. They can be very effective on a given instance of a problem and, at the same time, show long running times on another without finding a satisfactory solution. On the other hand, for example, the selection sort algorithm could spend different amount of time on an already sorted list, and on a list sorted in the opposite order, but we know that, on any list permutation, its time complexity function T(n) will be bounded by a seconddegree polynomial and the list will be sorted correctly.