Database corruption. How? Leading to bcheck.

Hi all, What reasons can you think of that can cause an Informix database to get corrupted such that it is necessary to use a bcheck to resolve any issues? The only sort of thing I can come up with are computers crashing while users access the database or poor quality programs and/or database administration causing poor quality data to bypass Informix's in built tests to make sure data and indexes don't occur. Any contribution to this issue would be extremely very welcome. Thank you, Ian.