This tends to be used when someone, who on being informed that they've caused offence, exclaims they did not intend to. Point being, ones intentions though worthy of consideration, in the end do not stop anyone being offensive.
I suppose it's similar to ignorance is no defence.
The lack of magic in ones intentions also works for the collapsing of intending to become slim, with the ability to become slim. i.e. Anyone who's slim intended to be so just as anyone not slim intended either, not to be slim or actively to be fat/ter.
This is another psychological tic produced by insisting weight is wholly in our direct control. As that always remains the same, the picture has to revolve around that, forcing any flexibility back onto the person.
An intention to become slim, however fanatical and long lasting is not the active agent in changing weight status.
Intent to lose weight cannot overcome biological design.