My motto: Never fail to block. Never.
I got gauge for the Arlo Sweater on the first go round. It was totally amazing. This NEVER happens for me. And so I set off on my merry way, knitting, knitting, knitting. I was a little bit worried because the back looked a little bit shrunken and sketchy. And then the miracle happened.
With a gentle block, the back measures just a bit bigger than my gauge swatch suggested it would be after blocking. This makes sense as the piece will ease back in a bit after the pins are out. Aren't the cables pretty after blocking?
Had I knit this one, using an unblocked gauge swatch, it would have been a disaster. Midway through my Godzilla sized sweater I would have run out of yarn. If you want to worship at the feet of the yarn goddess, you must swatch. And you must block.
The moral of the story? Swatch. Block. And knit happily every after.