If An airline is "countable", this means that there MUST be a flight attendant present on the plane, whose sole job is to count: In case of IEnumerable, only lines up to the element of interest will be read from the file. In case of ToList call over the enumerable, https://andresvzyzz.blogdeazar.com/28144923/bir-unbiased-görünüm-c-ienumerable-temel-Özellikleri