Here's why:
* Incomplete thought: "Cogitate" means to think deeply. The phrase "I cogitate that..." implies that you are thinking about something, but it doesn't tell us *what* you're thinking about.
* Missing object: The verb "cogitate" usually takes a direct object. You need to add the object of your thought to complete the sentence.
Example:
* Incorrect: "I cogitate that..."
* Correct: "I cogitate that the meaning of life is a complex question."
To make the sentence grammatically correct and meaningful, you need to provide the object of your contemplation.