Due Care/Reasonable care
Most insurance policies contain a clause specifying that the insured must exhibit 'due care' or 'reasonable care' or they will not pay out.
This generally means that policyholders must keep all of the property covered by a policy in good condition, and take reasonable steps to prevent loss or damage.
For example if the policyholder leaves the engine running in their car while it is unattended and the car is stolen, the car insurance provider may not pay out – as it could argue that the insured had not taken 'reasonable steps' to protect it and therefore breached the 'due care' clause in the contract.