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 think you mean "vain".
for no point
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)
To die in vain means that you died for a cause but your death did not change anything.
Without effect or to no purpose
Conceited means having an excessively favorable opinion of one's abilities, appearance, or accomplishments. It implies being vain or excessively proud.
Vain
Obsessed with looks
That you lived and died for no purpose.
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.'