Uncertainty principle
When humans measure some process on the subatomic scale and the uncertainty principle manifests itself, then human action can be said to have influenced the thing that was being measured. Making a measurement intended to get a definite indication of a particle's location will inevitably influence its momentum and whatever is done to measure that momentum as soon as possible after measuring its position, the probabilities of what momentum will be discovered cannot fail to have been changed. So the uncertainty principle can explain some kinds of interference produced by investigators that influence the results of an experiment or an observation. However, not all observer effects are due to quantum effects or the uncertainty principle. The remainder are "observer effects" but not quantum uncertainty effects.