In Spanish, it is not always necessary to include a subject pronoun before the verb because the verb endings themselves often indicate the subject. This is because Spanish verbs are conjugated according to the subject they refer to, making it clear who is performing the action. Including a subject pronoun can be done for emphasis or clarification, but it is not required for basic understanding or grammatical correctness.
For example, let's consider the sentence "Yo estudio español" which translates to "I study Spanish." In this case, the verb "estudio" ends with "-o," indicating that the subject is "yo" meaning "I." Therefore, including the subject pronoun "yo" is not necessary because the verb ending already indicates the subject.