Principle of indemnity: a claim should put you back where you were before the loss (make you whole), not leave you better off. Otherwise people would have a reason to cause losses. Life insurance is usually treated as a valued contract: because a human life cannot be priced, the policy pays the stated face amount.
Utmost good faith: both sides must deal honestly. The insurer relies on what the applicant says, so fraud, misrepresentation and concealment are prohibited.
Concealment, California rules:
Concealment, whether intentional or unintentional, entitles the injured party to rescind the insurance (§331).
Materiality is judged not by what later happened, but only by the probable and reasonable influence the facts would have had on the other party in evaluating the contract or making inquiries (§334).
Unless asked, neither party has to volunteer: facts the other already knows; facts the other ought to know with ordinary care; facts the other waives; facts that prove a risk excluded by a warranty, or relate to a risk excepted from coverage, and are not otherwise material (§333).
Neither party has to share their own judgment on the matter, even if asked (§339).