we have a fairly good idea.

Not scientifically. Humans act within an immensely complex multi-variate system. We aren't remotely close to thoroughly decorrelating the variables in observational studies (it may never be possible) nor do we have accurate prediction models for anything other than extremely narrow contexts.

And of course humans are animals, but we possess cognitive abilities very different to other animals. There's also an immense amount of animal behaviour that we simply do not understand.