This question already has an answer here:
I'm confused with when to use a comma or semi-colon when a word is repeated for emphasis because it's a general rule if you are to write two independent sentences together, they must have a conjunction to join them or a semi-colon. Yet, on Facebook or other writings I always see a comma used.
For example, Let's say I'm repeating "I". Is it:
I am the best; I am strong; I am dangerous.
I am the best, I am strong, I am dangerous.
The car is black; the car can fly; the car is wet.
The car is black, the car can fly, the car is wet.