From the research, the answer is clearly 'yes;' it is more difficult to formulate and follow rules than to use discretionary decisions. Discretionary decisions are ad hoc and tied to situations; they don't necessarily require consistency from one instance to another. Rules hold across time and situations (or they must be changed).
The rules versus discretion seems to apply in many domains from parenting and interpersonal relationships to macro-economic policies of government. Here's an example from Cafe Hayek.
"John Taylor: lays out the case for rules vs. discretion and in the process, does a superb job of summarizing his case for why doing less or even nothing would have been better than the activist government response over the last two and a half years. At issue is economic policy by the government.
One of the interesting questions Taylor raises in his paper is why what seemed to be a consensus in favor of rules changed so quickly into a consensus in favor of massive intervention."
If rules are more difficult than discretion, then I would wonder if the reason following rules might be more difficult than using discretionary decisions is the difference in cognitive complexity between the two. Rules require a reflective abstraction that pulls out the more general form and moves mental activity towards explanatory thought, the principles that underly economic activity and in this case of political economy the role of government in attempting to produce changes in general economic functioning.
We know from research on the grasp of consciousness that to envision results or end goals is easier than grasping the method of production. In elementary mathematics, children first can combine two sets to produce a third without conceptualizing the operation itself. They "add" two numbers to "get" an answer, and even their interpretations of equations with a missing numeral show they are focused on the answer. If they see two numerals with + and = signs, 4 + __ = 7 they combine the two numerals, 4 and 7, without regard to the meaning of the operations.
What we find is a development from simple, one-way actions directed to a goal which are oriented by a functional and practical focus to a more advanced form. The advance consists not only of combining operations to form a rational system of reasoning marked by logical necessities but also an increasing awareness of the methods of production as opposed to the outcomes.
