Through observing behavior, interviewing org members, and examining org documents, performance programs can be discovered. Knowledge of these programs provides large predictive power. Actors are constrained by themselves- believe it or not, this was hot stuff back in 1958. Where search for new alternatives is suppressed, program continuity is facilitated. The main requirement of actors in an organization is to satisfy situational criteria, not optimize, with criteria possibly shifting over time.
Bounded rationality appears here again.
Humans have realistic limits on planning capacity- cognition plays a large role in organizational change, from discovering problems to offering solutions to implementing them. Their book is a very long-winded way of stating this, but that is its primary goal.