According to Investopedia, perfect competition rarely exists because most industries almost never follow the five requirements of perfect competition. These requirements are that all of the firms make identical products; have small market shares; are price-takers; open information to consumers; and offer freedom of entry and exit.
Investopedia notes that most products have some differentiation, citing how water bottles differ in size, brand recognition and purification. In addition, most industries have barriers to entry. An example is the manufacturing industry, which has high start-up costs. The agricultural industry is the closest manifestation of perfect competition due to its well-informed commercial buyers and low barriers to entry.