Psi ability is viewed as the product of evolution, of the same processes of natural selection that has yielded human beings all other features and abilities.
Darwinian Theory has a base explanation for any ability: it serves to help human beings survive and pass on their genes to the next generation. The base explanation here is survival in the biological sense (i.e. the survival of the gene rather than the being).
Psi is assumed to be need-serving, and these needs are significant as they contribute to the health and well-being of the individual so as to make the individual better able, and more likely to reproduce to ensure the passing of genes.
One may take the term “survival” to assume psi is only useful in a critical moment collective with a critical need, but the term “survival” should be understood to mean more plainly: the ability to endure on a daily basis, to withstand hardships and stress (i.e. to be well).
Considerations include the implication that the individuals subconscious will know, typically subconsciously, in what circumstances psi may or may not be needed. Again, this is not to assume psi can only be used in critical situations or that any event in which can be attributed to the application of psi must have a need behind it, but this does seem to be the case.