If I'm not sore the next day, I consider the workout to be a waste. There's a difference between pain and soreness (well, maybe not to a noob). Pain is when you feel you MCL or hamstring tear (I've had both). Not being able to walk due to an excrutiating leg day is just soreness. So maybe it should be no sore, no gain. Again, though, the phrase is appropriate for noobs because to them soreness is pain, because they arent at the level they can enjoy it and bask in it.