The excessive time spent in searching is almost entirely spent on failures (sequences of operators that do not lead to solutions). If the computer could be made to look at promising sequences first and avoid most of the bad ones, much of the effort of searching could be avoided.
Blind search methods try operators in some fixed order, without knowing which operators may be more likely to lead to a solution. Such methods can succeed only for small search spaces.
Heuristic search methods use knowledge about the problem domain to choose more promising operators first.