This theoretical essay aims to investigate the existence of general contours for an economic-legal theory of imperfect long-term contracting, within the scope of non-mature jurisdictions, in Private Sector Participation (PSP) contracts. To achieve this objective, we follow a set of methodological steps: first, we describe the paradigm of the Arrow-Debreu World (ADW), in which long-term contracting is endogenous to opportunities, generating an ergodic environment of administrative contracting, which is no longer consistent with the economic-legal structure of infrastructure projects. As a second step, we have relaxed the major premises of the ADW, notably regarding ergodicity, contractual completeness, rational expectations, among others; in addition, we defined a Standard Administrative Contract (SAC), in a derivative of French civil law tradition, assuming a standardized risk allocation matrix, in which the operational, investment, demand and capital risks are allocated to the concessionaire, while the public partner bears the risks of force majeure, fortuitous event and factum principis, and the demand risk is fully allocated to the concessionaire even when the sources of the demand variation arise from macroeconomic actions. Subsequently, we have created three scenarios for the unfolding of demand, which is the main source of involuntary results for the concessionaire: adverse scenario, business-as-usual scenario (BAU) and benign scenario; we evaluated the consequences of the adverse scenario, seeking to understand the incentives for contracting, ex ante, in view of the possibility of its materialization. We work on the distinction between the concepts of flexibility and adaptability within the scope of long-term administrative contracts. Our essay concludes that, in a non-Arrow Debreu environment, with certain specifications on the existence of liquid markets for hedging certain risks (x, y, z), permeated by non-ergodicity, by the limited rationality of the agents, by the opportunism of the parties, the ex-ante incentive to contract depends on the adaptability of the contractual renegotiation, notably for the exploration of specific assets. Full flexibility of contractual renegotiation would incentivize opportunism; on the other hand, adaptability (a pre-ruled amount of flexibility) would increase ex-ante incentives to contract without a dangerous increase in opportunism. It is also concluded that, under the axiomatics and the postulates presented, the validity of Klink Boat Theorem (KBT) is a possible analytical solution to, in the face of a positive probability of materialization of events qualified as "uncertainties", still have an incentive, ex ante, for long-term contracting without the production of an adverse selection of bidders. The KBT's statement is: "in a non-Arrow Debreu environment, with limited existence of liquid markets for hedging certain risks, in a non-ergodic environment and limited rationality of the agents, in the presence of market failures typical of strong informational asymmetry and property issues (indivisibilities à-la natural monopoly), the current incentive system will lead to actual contracting of long-term concessions if there is adaptability for contractual renegotiation in the event of the materialization of the most adverse economic scenarios to the contract". This adaptability solution can be extended to the various situations in which the uncertainties of the original negotiation (elements not contemplated by the risk matrix) effectively materialize, changing the starting conditions on which the contracting was based.