The words inciteful, insightful sound the same but have different meanings and spellings. Why do inciteful, insightful sound the same even though they are completely different words?
The answer is simple: inciteful, insightful are homophones of the English language.
That incites, or provides incitement
Showing or having insight; perceptive.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.