I think a lot of people spent their childhoods being very deliberately forced out of their comfort zones by parents / teachers / whomever in a way that was just deeply unpleasant and degrading and so, when they reach young adulthood and are finally allowed real control over their lives, become set on only doing things they know they're comfortable with forever. that's a really important thing to be able to do, especially if you're so used to having your boundaries routinely ignored that you aren't even certain what you like vs what you can bear, so I absolutely see why a person would have a negative reaction to being told that discomfort is good: it can very easily sound like being told that all that work they've been doing to prioritze their needs for the first time ever is Bad and Selfish, actually. and to that I will say two things:

“All of us blossom when we feel loved and wither when we do not feel loved.”

“You need someone who goes out of their way to show they need you in their life.”