This is not necessarily the case for every one. Flat iron works most of the time. One just needs to take precaution so that you not pull your hair too much. If this treatment hurts the root then you need to stop it at once.

this is funny

flat irons are used for straightening the hair! it doesn't act like a hair dryer, hence shouldn't be used to dry the hair

sure it makes the hair dry out but use a serum, it should work fine then and your hair will turn out sleek and shiny