AHA! I have figured it out, finally.
68It can only discard skills among the selectable ones that turn, the previewed skills can't be discarded meaning if you discard an S1 and then an S3 with S2 and then use an S1 on your 2nd skill slot the S1 keeps the insight buff from the discarded S3 because it can't discard the previewed skills.
This can very easily get messed up if your S1 gets used first for some reason since it discards the S3 first making the S2 discard an S3.
Never bothered learning it from Dieci Rodion since she only discards 2 slots if she uses an S3, which I usually discard for S1 buffs and shield.
Next up is trying to make use of his passive to get buffed S3's since that's the only move that can benefit from insight increases because all other moves replace said insight with a discard.
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