If you are bound by a particular text's answer, I would caution you to study this and place others' suggestions in that context. I think that the loss of New York as well as the early stages of frustration for Colonial forces reflected the lack of international support and the overwhelming challenge of battling the British. The early challenges faced by the Colonial army were to be expected from a short term perspective in fighting the British. It was only when the conditions of battles such as Saratoga and Valley Forge when we start seeing the British plan of attack begin to falter as the Colonists were able to make more use of international support as well as knowledge of their own geography over the British use of intelligence. I think that the loss of Long Island and other setbacks in the early phases of the war reflected this lack of understanding about how victory was to be achieved as well as a lack of resources from the international community.