Learn English – Antonym of “advance”

The problem here is that the idea of "opposite" is not analogous to a logical negation.

Consider a scale from −10 to 10, and let us define the property good as anything greater than or equal to 9. The negation of good— not good—would of course be anything less than 9. On the other hand, "opposite" suggests the inverse of the property; the same property reflected symmetrically about some pivot onto the opposite end of the spectrum. Hence the "opposite" of good in this case would be anything less than or equal to −9.

While indurated and hardened are probably better when you're intending to exaggerate (although indurated is not in common usage and sounds somewhat pompous), I would recommend the phrase used to:

"I've gotten used to wearing uncomfortable shoes; I can wear anything on my feet now"

is the most common opposite of

"I've been spoiled by these comfortable shoes, I can't wear anything else now".