Firstly, the agent may be risk-averse, so there is a trade-off between providing the agent with incentives and insuring the agent. Secondly, the agent may be risk-neutral but wealth-constrained and so the agent cannot make a payment to the principal and there is a trade-off between providing incentives and minimizing the agent's limited-liability rent. Among the early contributors to the contract-theoretic literature on moral hazard were Oliver Hart and Sanford J. Grossman. In the meantime, the moral hazard model has been extended to the cases of multiple periods and multiple tasks, both with risk-averse and risk-neutral agents.