Despite this recognition of decision making by project managers, many project managers often make poor decisions. "Poor" decisions by project managers often share characteristics.
A failure to consider the behavioral consequences of their decisions. When they do, they take inappropriate action to mitigate the consequences. For example, some project managers decide unilaterally to change a course of action. Under certain circumstances, making such a decision may be appropriate. In other words, it can cause people to perform rework or seek additional skills. Failure to account for such consequences can deteriorate morale and esprit de corps.
Adherence to a short- term perspective. Because many projects move fast, such as fast-track development projects, project managers feel pressure to succumb to a quick fix. Sometimes, however, the quick fix may lack wisdom and represents a failure to consider looking at downstream impacts, e.g., rework and delays. Impacts augment frustration and tension to an already frustrating and tense experience. In Why Decisions Fail , Paul Nutt describes the consequences quite clearly in the general context of decision making. He says that people who make decisions often grab the first idea and then try to make it a reality.  Ian Mitroff agrees and notes that it is a serious shortcoming of management in general, and observes that most management errors are predicated on addressing either the wrong issue or an unclear one. 
An inability to distinguish between major and minor issues and information. Some project managers consider everything equal when in reality that is not true. Not surprisingly, these projects fall into an analysis paralysis mode, awaiting definition and verification of everything. When making a decision, it becomes an anachronism, losing its relevancy and significance.
A failure by some project managers to focus on the goals and objectives of their projects. When focus is lost, the opportunity for "scope creep" increases . Scope creep is the inadvertent expansion of goals and objectives; it often occurs by accident rather than design. Failure to direct decision making from the context of the original goals and objectives can have disastrous effects on performance, e.g., excessive overtime, burn out, and missed milestones.
Introduction of bias. Bias can come from the project manager alone or from other stakeholders, such as senior management or a customer. The impact of bias can be tremendous and can result in overlooking essential information; failing to consider different, perhaps more important alternatives; and being overly optimistic or pessimistic. What complicates bias is the difficulty in detecting it, especially personal bias. Whether detectable or not, biases can cause silence when people should speak up; overlook important information; and play "favorites" among team members . Stephen Covey observes quite correctly the powerful influence of bias in decision making and the problems accompanying it once it was in the form of a paradigm. He says that everyone has "maps" within their brains that divide everything into what is and what should be. The maps are very powerful because people interpret everything with them and they are seldom questioned. All subsequent attitudes and behavior reflect these maps. 
Failure to seek feedback on effectiveness. Without feedback, project managers will be unable to ascertain effectiveness. Too often, many project managers not only make snap judgments , but also fail to conduct follow-up. If they do, they frequently do so to support their own decision. In other words, they allow bias, either by design or fault, which is a common problem in other management levels. Paul Nutt says that some decision makers will continually re-evaluate with the intent of defending their decision to show that it is feasible or that it was the right one. Such efforts can prove costly in terms of time and money. 
 Paul C. Nutt, Why Decisions Fail , Berrett-Koehler, San Francisco, 2002, p. 5.
 Ian Mitroff, Smart Thinking for Crazy Times , Berrett-Koehler, San Francisco, 1998, p. 7.
 Stephen R. Covey, The Seven Habits of Highly Effective People , Simon & Schuster, New York, 1990, p. 24.
 Paul C. Nutt, Why Decisions Fail , Berrett-Koehler, San Francisco, 2002, p. 6.