Final answer:
The psychological concept is the Sunk Cost Trap, where Elger's decision to maintain a friendship due to past investments like buying coffee, illustrates an irrational commitment influenced by previous expenditures.
Step-by-step explanation:
The psychological concept discussed in lecture that is portrayed when Elger decides to maintain a friendship with Danya because of all the coffee he has bought her is the Sunk Cost Trap (also known as the sunk cost fallacy). The sunk cost fallacy occurs when a person continues a behavior or endures an activity due to the significant investment they have put into it (time, money, or resources), even when this continuation might not have intrinsic value or the outcome is no longer beneficial. This is in contrast to making decisions based solely on the present and future benefits and costs.In Elger's case, the coffee he has bought for Danya represents a past cost, which should not influence his current decision to remain friends. However, his decision is influenced by these past expenses, illustrating the sunk cost trap. The rational decision would be to ignore the past investments and evaluate the continuing worth of the friendship without the weight of the sunk costs.