The most persistent rumor is that if you present a koala with a plate of eucalyptus leaves, it will not eat them, failing to recognize them as food. This is often cited as proof of their stupidity.
The most common evidence cited for a koala's lack of intelligence is its brain. In most mammals, the brain is folded with wrinkles (gyri and sulci) to increase surface area for neurons. The koala, however, possesses a remarkably smooth brain. Koala brain - Comparative Brain Anatomy dumb koala
In the harsh Australian bush, where water is scarce and food is poisonous, the koala is not stupid; it is a biologically efficient machine. It does not need to do math or recognize plates of food; it just needs to sleep, detoxify, and climb. By those metrics, the koala is an evolutionary genius. The most persistent rumor is that if you