  In order to explain the empirical evidence that the dynamics of human
activity may not be well modeled by Poisson processes, a model based on queuing
processes were built in the literature \cite{bar05}. The main assumption behind
that model is that people execute their tasks based on a protocol that execute
firstly the high priority item. In this context, the purpose of this letter is
to analyze the validity of that hypothesis assuming that people are rational
agents that make their decisions in order minimize the cost of keeping
non-executed tasks on the list. Therefore, we build and solve analytically a
dynamic programming model with two priority types of tasks and show that the
validity of this hypothesis depends strongly on the structure of the
instantaneous costs that a person has to face if a given task is kept on the
list for more than one step. Moreover, one interesting finding is that in one
of the situations the protocol used to execute the tasks generates complex one
dimensional dynamics.
