Big +1. And there is lots of research on the placebo effect confirming the above. Which is why for most academically recognized scientific research involving humans a double blind study is required and the papers are subsequently peer reviewed and blind tests involving experts in anything that qualitative, whether it be wine tasting, audiophile products, guitar gear, etc, invariably makes the experts look like idiots.
It's also why forum opinions, youtube video comments, clip postings, etc, are for the most part meaningless.
Sometimes I'll try to close my eyes when listening to A/B comparisons, etc, but even then if the person performing can see the gear, it will affect their performance, etc, so it's hardly any kind of substitute.