Ensure vs Insure
Quick answer: Ensure means to make certain something happens. Insure is the financial one — covering something with an insurance policy. You ensure success; you insure a car.
Ensure
Verb: to make certain; to guarantee.
“Check twice to ensure the door is locked.”
Insure
Verb: to cover with an insurance policy.
“The house is insured against flooding.”
How to remember it
INsure = INsurance. Everything else, ensure.
Common mistake
'Insure you arrive early' — no policy involved: ensure.