Take this post with a grain of salt

Why does taking something with a grain of salt mean taking something with a degree of skepticism? Basically, if you can eat bitter food more easily with a small amount of salt, then lies or shady claims can be mitigated by a grain of salt.

In 77 AD Pliny the Elder, in his encyclopedia Naturalis Historia, translated the recipe for an antidote to poison by stating to "take two dried walnuts, two figs, and twenty leaves of rue; pound them all together, with the addition of a grain of salt; if a person takes this mixture fasting, he will be proof against all poisons for that day."