Culture shock is the loss of emotional balance, disorientation, or confusion that a person feels when moving from a familiar environment to an unfamiliar one. When it is a common experience, the degree to which it occurs will vary from one person to another. Individual personality, previous cross-cultural experience, and language proficiency all affect a person's ability to interact socially in the new culture. The basic cause of culture shock is the abrupt loss of all that is familiar, leading to a sense of isolation.
When an individual enters a strange culture, all or most of those familiar signs and hints are removed. He or she is like a fish out of water. No matter how broad-minded or good-willed he may be, a series of properties have been knocked from under him. This may be followed by a feeling of frustration and anxiety. People react to the frustration in much the same way. First they reject the environment which causes the discomfort: "The ways of the host country are bad because they make us feel bad."
Another aspect of culture shock is regression. The home environment suddenly assumes a tremendous importance, and everything becomes irrationally glorified. All difficulties and problems are forgotten and only the good things back home are remembered. It usually takes a trip home to bring one back to reality.
Common symptoms of culture shock include the following extremes. These are excessive concerns over delays and other minor frustrations; fear of being cheated, robbed or injured: sleeplessness or a desire to sleep more; and a great longing to go home. Underlying all these is the uncomfortable feeling of not really belonging, of being an outsider.

Diffusion, the process of introducing cultural elements from one society into another, occurs in three basic patterns: direct contact, intermediate contact, and stimulus diffusion.
In direct contact, elements of a society's culture may be adopted first by neighboring societies and then gradually spread farther afield. The spread of the manufacture of paper is an example of extensive diffusion by direct contact. The invention of paper is attributed to the Chinese Ts'ai Lun in A.D. 105. Within fifty years, paper was being made in many places in central China. By 264 it was found in Chinese Turkmenistan, and from then on the successive places of manufacture were Samarkand (751), Baghdad (793), Egypt (about 900), Morocco (about 1100), and France (1189). In general, the pattern of accepting the borrowed invention was the same everywhere. Paper was first imported into each area as a luxury, then in ever-expanding quantities as a staple product. Finally, usually within one to three centuries, local manufacture started.
Diffusion by intermediate contact occurs through the agency of third parties. Frequently, traders carry a cultural trait from the society that originated it to another group. As an example of diffusion through intermediaries, Phoenician traders spread the alphabet which may have been invented by another Semitic group, to Greece. At times, soldiers serve as intermediaries in spreading a culture trait. During the Middle Ages, European soldiers acted as intermediaries in two ways: they carried European culture to Arab societies of North Africa and brought Arab culture back to Europe. In the nineteenth century Western missionaries brought Western-style clothing to such places as Africa and the Pacific Islands.
In stimulus diffusion, knowledge of a trait belonging to another culture stimulates the invention or development of a local equivalent. A classic example of stimulus diffusion is the creation of the Cherokee syllabic writing system by a Native American named Sequoya. Sequoya got the idea from his contact with the English; yet he did not adopt the writing system nor did he even learn to write English. He utilized some English alphabetic symbols, altered others, and invented new ones.