Well...You just need to know what vain means.'It is vain to do with more what can be done with fewer.'or'My sister is so vain that she talks to herself in the mirror.'or'Some people are vain enough to laugh at ugly people.'
To do something in vain means that you do not succeed in doing what you are trying to do; to try in vain is to fail.
in vain means the expected result is not going to happen
i have made mistakes in my lide, but i know now what i could of have done differently so why live dwelling over it.
I think you mean "vain".
To die in vain means that you died for a cause but your death did not change anything.
Vain means conceited, or it may mean to no avail. Here are some sentences.She tried in vain to stand on her head.He was as vain as a peacock."You're so vain!" (a song by Carly Simon)
Without effect or to no purpose
Vain
Obsessed with looks
That you lived and died for no purpose.
without success, or something done for nothing, as a waste of time and energy.