What is the "process of nature" rule in the context of a disability claim?

"The 'process of nature' rule holds that, within the meaning of policy provisions requiring disability within a specified time after the accident, the onset of disability relates back to the time of the accident itself whenever the disability arises directly from the accident 'within such time as the process of nature consumes in bringing the person affected to a state of total (disability).' (Schilk v. Benefit Trust Life Ins. Co. (1969) 273 Cal.App.2d 302, 307 (78 Cal.Rptr. 60) ....)" (Willden v. Washington Nat. Ins. Co. (1976) 18 Cal.3d 631, 635, 135 Cal.Rptr. 69, 557 P.2d 501.)