Why Is It Usually Advantageous to Place Key Issues of the Negotiation

Why is it usually advantageous to place key issues of the negotiation near the end of the agenda?

A) It provides an opportunity to learn the other side's bargaining style and concession routines.
B) It saves time if agreement can't be reached on the small stuff there is no need to discuss the key issues.
C) By conceding most of the smaller issues in the early going, the selling team creates a moral "debt" which the buying team is likely to have to repay by conceding on the later, key issues.
D) It allows the team setting the agenda to wear down the other side which will then be more likely to agree as they become tired and are hurrying to conclude the negotiations.
E) Actually, key issues should be handled as early as possible in case some interruption prevents finishing the agenda.