TL:DR – The chemical ionone gives violets their scent, but the scent temporarily fades if you keep sniffing the flowers.
Savour the scent of violets for too long and the smell will eventually fade. In fact, you won’t be able to smell anything for a while after until the chemical, ionone, that give violets their scent has dissipated from within your olfactory cavities.
The combination of ionones gives violets their sweet but dry and powdery smell. These chemicals (also known as rose ketones) have an interesting effect on your olfactory receptors, inhibiting them after initially stimulating them and this steals away your sense of smell. This was an effect that was once considered magical and immortalised in folklore for generations. But, it’s much more magical than anything supernatural, it’s chemistry!