Here's why:
* "But" and "and" are conjunctions, and conjunctions connect words, phrases, or clauses.
* When they start a sentence, they're part of the independent clause, which is the main part of the sentence and doesn't require a comma.
Example:
* Incorrect: But, I like the color blue.
* Correct: But I like the color blue.
* Incorrect: And, the sun is shining today.
* Correct: And the sun is shining today.
However, there are exceptions:
* If the sentence is very long or complex, you might use a comma for clarity.
* If the sentence contains a parenthetical phrase after "but" or "and", you would put a comma before and after the phrase.
Example:
* Correct: But, as I mentioned before, I like the color blue.
* Correct: And, believe it or not, the sun is shining today.