I hope this thread gets read by everyone who feels like a failure because the scale doesn't march downward cooperatively by a few ounces every day like clockwork!
I rarely get on the scale before bed, but sometimes I do after I come home from the gym and before eating dinner - and I typically find my weight at that time is 2 pounds higher than it was that morning. Then my dinner has its own weight, say about a pound, not to mention 1-2 pints of water that I drink in the evening as well. I wouldn't be surprised if I typically go to bed weighing 4-5 pounds more than I did that morning.
And yet aspiration, perspiration, elimination, all those marvelous process bring my weight by morning more or less down to where it was the previous morning, give or take a pound or two. Amazing!
As for morning-to-morning fluctuations - when I first started on my eating and exercise plan, I could see daily bounces of as much as 4 pounds (which could mask a whole lot of fat loss, let me tell you) - depending upon what I'd eaten the previous day, what I drank, how much hard exercise I'd done, etc.
Nowadays I rarely see a bounce of more than 2 pounds up from day to day - although a 2-pound bounce is pretty common.
I weigh every day, but I measure success on a time scale of many weeks.