Firstly, Jamestown was the first English settlement in North America. Unfamiliar with the terrain and climate of the region, the settlers at Jamestown were woefully unprepared.
Jamestown was established on a river about 30 miles from the Chesapeake Bay. This was a low-lying, marshy area that lacked fresh water. Furthermore, the summer weather lowered the river level and brought in saltwater. This led to the spread of typhoid, dysentery, pneumonia, and other diseases.
The men employed by the Virginia Company were sailors not trained to farm, hunt, or work in the wilderness—all of which were skills required to establish a functioning colony in the 1600s. Additionally, the colonists expected a more amiable relationship with the Native Americans that would result in bountiful trade.
Unhappiness is Jamestown led to constant conflict, and leadership was poor until John Smith took control. However, his approach was largely dictatorial, resulting in his famous philosophy of "He that will not work shall not eat."