No fix is perfect. Here's what this pattern won't handle:

• If you sweat heavily during your commute, the salt and moisture can weaken fibers over time. Rinse the collar with cold water when you get home, even if you're not washing the whole tee.
• If your backpack strap is particularly rough (like a heavy-duty hiking pack), consider adjusting the strap so it sits on your shoulder, not your collar. Or wear a collarless layer under the pack.
• If you're washing a new tri-blend for the first time, the first wash is the most critical. Follow the inside-out rule from day one.
• If you air dry but the collar still looks worn, check your detergent—some enzymes are harsh on rayon. Try a gentler, liquid detergent.

These edge cases don't change the core fix; they just cover the rare situations where friction isn't the only culprit.