Why do Traditional Economics assume that Economic Agents [Producers, Workers and Consumers...] act Rationally?

-This can be based on the Assumption that Economic Agents want to Maximise their Utility [Well-Being] -Different Economic Agents will have different Ways and Targets to Maximise their Utility: Consumer with Value; Producer with Profit -This means Decisions have to be made on the Basis that it will Gain the Most Utility more: Nothing else will Influence that Decision