Make an error once, and you can bet you'll make it again. Why? Habit and generalization.
First, habit. I can explain that sentences need to be concluded with closing punctuation such as periods, question marks and exclamation marks, but if you've been concluding them with commas for the past several years -- or decades -- you're likely to continue the practice. It's a matter of habit, and habits are hard to break.
This sentence is correctly closed with a period. This one is not, it's "spliced" to the following sentence (the one you're now reading) with a comma. For this reason, the preceding two-phrase sequence is called a "comma splice."
Understanding this explanation, however, is not enough to eliminate the error. You need to break the habit.
The second reason you're likely to repeat your mistakes is generalization, the tendency to apply wrong assumptions broadly.
Let's say you're in the habit of creating comma splices around the adverb however, as in, "I'm furious about the ambush marketing near the gorgeous new Twins' ballpark, however, there's nothing I can do about it." Your erroneous assumption is that however serves as a conjunction or connecting word like but, and therefore no closing mark is needed after ballpark. Having made this wrong assumption, you're likely to apply your faulty thinking broadly. If it's all right to use however with commas between two complete sentences, you assume, then it's all right to use therefore with commas between two complete sentences, as in "We want to make money by advertising, therefore, we'll do what we damn well please." As every good editor knows, if a writer serves up a however comma splice, a therefore comma splice is not far behind.
Habit and generalization. They're what stands between many writers and clean copy.
The solution? Exercise and patterns.
To eliminate a habitual error, you need to do more than understand why it's wrong. You need to practice correcting the error. The way to get that practice is by doing exercises. For example, which of the following sentences are correctly punctuated? Which contain comma splices?
1. "You may not think we have the right to make money by placing massive signs anywhere we please, nevertheless, we're going to do it."
2. "You can create a beautiful gathering space if you like, but don't expect us to respect it."
3. "I believe that offending the public is a bad way to advertise a product, however, I may be wrong."
Did you correctly identify 1 and 3 as having comma splices? Do you understand how the conjunction but in 2 correctly joins two sentences into a single compound sentence?
Now for some good news. By doing your exercises, you begin to recognize patterns. The result: Your writing improves exponentially. You don't eliminate single isolated errors; you eliminate entire categories of errors.
For a list of 75 common errors, organized by category for systematic elimination, see www.wilbers.com/ErrorChecklist.htm. Now, if I might propose some community-conscious values in advertising ....