Whenever possible, write positive statements, which are much more powerful and easier to understand than negative ones.
Compare the impact of the following pairs of sentences:
“The intersection is not dangerous.”
“The intersection is safe.”
“He did not arrive on time.”
“He arrived late.”
“She did not remember the number.”
“She forgot the number.”
“They did not pay attention to the matter.”
“They ignored the matter.”
In general, sentences with the word “not” are weak. Words like “forgot” and “ignored” are ways to express a negative in a strong, positive form.
Also, it generally takes fewer words to state something positively than to state it negatively.
Interestingly, as The Elements of Style points out, “placing negative and positive in opposition makes for a stronger story.” One of the most famous examples of this is the oft-quoted statement from Kennedy’s inaugural address: “…ask not what your country can do for you – ask what you can do for your country.”