Stop a Thought
A period stops a thought. If you are describing how a person reacted to a situation, you don’t just ramble for line after line. You need to stop periodically to keep certain thoughts together. That is where a period comes in to play. Just look at what you are reading right now. Look at each sentence. They are standalone thoughts. All the sentences can work together, but they can stand alone. The period separates them.
I once read somewhere that a period is like a stop sign. It stops you as you read. Just like when you are driving, you stop and then proceed. That is what a period is.
Now, just because you see a ‘.’ doesn’t always mean it is a period. That same mark can be combined with other dots and create an ellipse. That is basically a mark showing that there is more to the thought. When alone, like you see here in this article, it is a thought stopper.
When Not to Use
That being said, there are times you don’t use a period when a thought is complete. That includes titles, headings, subtitles/subheadings, or after an abbreviation. These are the times you don’t need the all-important comma. They can stand on their own.
Periods are rather easy to use. It’s that blasted comma that gets you every time.