A can made out of a
tin like metal (usually
aluminum) that looks and seems tough on the outside at a first glimpse, it's not until all the liquid drains out that people realize it
crunches and flattens like a pancake, and that it was always like that. The liquid was keeping it inflated the entire time.
The
beer can of a car they were riding around in seemed tough and
resilient until the first
accident. Until then, nobody thought there was anything dangerous about it.