Sightings are not evidence they exist. They are just evidence that someone thought they saw something that resembled a creature they know from folklore. Or they saw something they couldn't explain so used the yeti to explain it. They had a mental reference for it already in their imagination. Evidence can be fact or opinion. Someone saying they saw a yeti is just stating their opinion. In a forest people's imagination can play tricks on them. There's usually a rational explanation. A deer moving through undergrowth, a bear, a badger digging around tree roots making the tree mysteriously shake. A prey animal screaming as it's caught by a predator. It's like the Loch Ness Monster, Great for tourism and TV shows. If they existed we would have found, caught, or killed one by now, especially in Siberia because of all the people living in the forests and the military and oil and gas and mining workers. Stories of creatures dwelling in the forest were told to children so they didn't stray off the forest paths they knew and went exploring and got lost.