Winter is essentially a friction festival for your collar. Think about everything that touches that one strip of fabric between November and March: a wool scarf, a fleece zip-up, a denim jacket, your beard if you've got one. Each of those surfaces grabs at the short fibers in a tri-blend and pulls them loose. Once they're loose, they tangle into the pills you see.

It's not just the layers, either. Dry indoor heat and cold outdoor air both dry out the fibers, making them more brittle. Brittle fibers break off more easily when they snag, which adds to the pilling. So yes, it's the season, but it's also the fabric's nature.