If you are seeking to change someone’s mind, desperation should be a last-ditch effort in order to get your way. 

Changing someone’s mind requires the other person to go through the mental hurdles of admitting that their initial assertion was incorrect, and that they should now believe something new. 

Desperation ends up signalling that you’ve admitted that the other person was right, but that you still want them to do/say something that they don’t truly believe or stand by anyway. 

Usually this will not only feel bad for everyone involved, but you’ll also probably not get your way either.