Design is difficult for three fundamental reasons.  First a perfect or best solution does not exist.  Unlike an algebra problem, no solution is the unique correct solution.  Instead many feasible solutions exist that possess characteristics that are better or worse than other solutions.  Is a Ford Focus a better transport solution than a Lexus?  The answer depends upon if you value prestige and comfort over low price.

Since there is no one crrect of perfect solution, designers must consider many different designs at once.  Therefore designers must be comfortable dealing with ambiguity.  This means that they must committ to a design before many alternatives are analyzed.  This can drive many beginner designers crazy!  Begginners often want to take their first feasible idea and move forward quickly and the resist studying alternative solutions.  This can lead to much wasted time if the designer discovers a better solution after spending valuable time and resources developing an inferior solution.

Finally, studies have shown that the most important decisions about the design of a product are made at the beginning of the design process.  For instance, a car designer must first decide very early in the design process if the car will be powered by an electric motor, a gas engine, a diesel engine or fuel cell.  Once this decision is made, the many other design choices can be made.  Unfortunately, this very important decision must be made at the beginning of the design process when the designer knows comparitively little about the design problem.  Conversely, design decisions with relatively little impact on the performance or reliablity of the design are made towards the end of the design process.  When the designer knows the most about the problem, he or she is making the decisions that matter the least!  Figure 1 shows the dilemma in a graph.

Figure 1. Time versus Knowledge or Impact.