L’appetit vient en mangeant
[The appetite grows by eating]
François Rabelais 1494-c1553
Gargantua et Pantagruel (1534) 1.v
In the context, ‘appetite’ means appetite for food. The truth of this is recognised by gastronomy – what else are appetisers, but food to make you hungry, give you an appetite where you had none before?
But in a metaphorical sense it applies to many things, like power…