Here's a truism for you: Only people who look up words they don't know can expand their vocabularies. Did you find that statement obvious, boring, and saying nothing new or interesting? That's the perfect description of a truism.
Sometimes truisms can be mistaken for factual statements. In fact, despite their seeming obviousness, they are usually opinions. Many people who look up words in the dictionary don't improve their vocabularies, as much as they'd like to. Another truism: You get what you pay for. Well, a lot of the time, sure, but not always. That's why the word bargain was invented.