Let's say someone has an idea that he/she thinks is really good, but in reality it is actually not a very good idea. How can I describe this kind of mentality?
"Foolish" or "Fool", "idiotic" is also good. Senseless is another fun term.
"Buying seventeen buckets of frogs is idiotic." "He's an idiot for snowboarding off the roof.", "That's the most foolish idea I've ever seen."
Senseless is ideal if the person making the bad decision has failed to account for most of the variables, and the repercussions won't be particularly severe. "He died senselessly while cleaning a plugged in toaster."