A lot of people confuse guarantee with warranty.

"I guarantee this will last a lifetime" Means no conditions, no questions asked. Manufacturers do not give guarantees. They give warranties.

A Lifetime Warranty is your assurance that should the product fails due to a defect in the manufacturing or the materials, it will be replaced or repaired once a determination has been made that the failure was not due to misuse, abuse or poor maintenance and providing that claimant can prove they are the original owner of the product.

A warranty has several loopholes big enough to ride a bike through. You usually have to pay for shipping it back to the manufacturer. If they deem it covered under warranty, don't expect a whole new bike, expect it back with the failed component replaced. You will have to pay for having it shipped back to you.

If the frame fails they will want the only the frame shipped to them for warranty evaluation. First the bars, stem, wheels, crank set,front and rear derailleurs, brakes, cables and misc. bottle cages must all be removed. Doing it your self or paying a shop to do it is on you and your dime.

If they rule in your favor and ship a replacement frame you are on the hook for paying a shop to put it all back on, or do it yourself.
If the manufacturer rules it was misuse, abuse, neglect, or poor maintenance you pay for them to ship the frame back if you still want it.

A warranty is a nice word to hear in a showroom and helps convince you to reach for your wallet.
It is not a guarantee.