Anything anyone ever told you about premium fuel.
"Give your car some premium fuel every now and then to clean out the engine."
"My dad used to put premium gas in it, so now I can't stop or it will hurt the engine."
"If you're not happy with your Corolla's power, put better fuel in it."
All of these things we've heard, and they're all crap. The truth is that if the engine in your car wasn't designed with a compression ratio that can take advantage of higher octane fuel, all you're doing is spending more money. Putting 87 octane in a car that needs 91 will hurt the engine, but putting 91 in a car that was designed for 87 will do nothing.