Rational decision making involves four basic steps:
1 Search for possible options
2 Anticipating outcomes in each option
3 Evaluation of each outcome
//Source: March, J., A Primer on Decision Making: How Decisions Happen, Free Press, New York, 1994
Humans are not always able to find all possible options, they don't have all information about possible outcomes, evaluation is subjective and linked to time, location, age preferences - so selection is based on a bounded rather that 100% rational process.
In designing peer-to-peer systems where human groups play role of rational agents one should take into account that at higher stakes the system could be confronted with a fully rational algorithm. Human groups organized with such algorithms loses their "crowd" qualities and become monolythic agents.