It seem like the sun never shines on Saturday.

The correct word in this sentence is "seems" instead of "seem." In standard English grammar, the subject "it" is singular and requires a corresponding singular verb form. Therefore, the verb must agree with the singular subject, which is why "seems" is the appropriate choice here. Using "seem" would create a subject-verb agreement error, as "seem" is a plural form. In this context, "it" refers to a general idea rather than a specific noun, so it necessitates the singular verb "seems" to maintain grammatical correctness throughout the sentence.