@Zenitsu Check out Human Behavior and the Principle of Least Effort. He has really interesting arguments that explain much of psychology.
For example, he defines intelligence as economy of action. We use as few tools as possible to perform as many jobs as possible. Intelligence is simply the jobs to tools ratio.
A mushroom seems stupid because we compare it to our job-space. To us, a mushroom performs few jobs: eat detritus, release spores.
It is only until we examine its full network complexity that we start treating mushrooms as if they were intelligent beings.
And the reason why difficult jobs seem more ‘smart’ is because they are jobs that we cannot perform. It represents a hard limit on our job-space.