Because being aware of oneself in the past, present and future all at the same time allows us to view and theorise about our impact on ourselves and our surroundings. Animals don’t do this, they run on stimuli and instinct and don’t stop to theorise whether they are hungry or they got stomach ache.
edit: I wanted to say humans have an internal voice, but not all humans do so while it’s a symptom of consciousness, I don’t think an internal voice is the cause/reason
Yes, exactly. I find that that is what distinguishes us from animals. “I am happy because of this cool new toy that I got gifted to me because it’s my birthday” versus “I am happy because I’m playing with this toy”