bounceswoosh
Ski Diva Extraordinaire
If we discuss this for long, @bounceswoosh or half a dozen others will recommend A Conversation with Fear, by Mermer Blakeslee. I haven't read it but when others quote it I am impressed with the science (and I'm usually very critical!).
LOL!
This is a good point, but I really do think instruction and "time on skis" are the factors here. Blakeslee's book is largely about gradually exposing yourself to what scares you, and finding ways to mimic those situations - like getting used to narrow runs by purposely skiing only 1/4 of an open run. I'm not sure how I would create that sort of scenario for slush.
For what it's worth, I only started getting comfortable with spring conditions a couple of years ago, and I ski a LOT. I also believe you need to engage a lot of core strength, and unless you are a pro, you benefit greatly from having built up your skiing skills all season long. If you ski a few times a season, I just am not convinced you're going to get there. ("You" = "one.")