Of course one can knit all year. And naturally, one can sit in the corner of the couch with a blanket in June. And light candles in april. But it all just come together so beautifully when the evenings darken, and the air gets colder.
One of the great great reasons I love the fall, is the curling up in the corner, with heavy socks on, a soft pillow, warm tea, and wool. Meters and meters of soft knittable wool. :)