Final answer:
The President rarely calls Congress into special session because Congress is usually in session, addressing issues continuously. Moreover, the President's unilateral powers such as executive orders reduce the necessity for special sessions. The power to summon Congress is reserved for 'extraordinary occasions'.
Step-by-step explanation:
The main reason that the President rarely has to call Congress into special session is that the function of Congress has evolved over time to be nearly continuous, with regular sessions throughout most of the year, reducing the need for special sessions. Furthermore, the President has various unilateral powers, such as issuing executive orders and making use of signing statements, which can be used to address issues without requiring a special session. However, these powers are not absolute and are subject to check by Congressional oversight, limiting actions the President can take without Congress.
Contrary to some of the provided options, the President does not have the authority to make decisions without Congress on legislative matters, and conflicting agendas between the two branches can often occur. Moreover, the relationship between the President and Congress can vary and is not always harmonious. Indeed, the President cannot simply call special sessions whenever desired; it is a power reserved for extraordinary occasions, which in practice has become rare due to the near-constant session status of Congress.