Which one wins?

Okay,

Two (among the many) tenets of lawn mowing is not to cut more than 1/3 of the blade and not to mow when the grass is wet.  I run across this conflict a lot through the year, and it just happened to me a short time ago and brought up the question again:  If its been raining off and on and the grass is getting too long to wait for a dry day, what's a mower to do?

This last time I mowed while still wet.  Made a mess of me, my mower, and some "laid down" places in the grass.  Perhaps I even opened up some areas to disease...?

So which of these two rules should win in a conflict?

I can't rightly comment on the long term effects. Our spring rainy season coincides with our dandelion bloom, and a growth spurt for the grass. I mowed the lawn 4 days in a row with it wet this year. I did this to keep the grass height in check, and take a whack at the dandies, which popped up new, huge crop of seeds each of those days. I bagged up their seed heads with the grass and am composting them. Now I had some areas of grass that laid down while it was wet due to my obsessive mowing. They all perked right back up in a couple of days. The trick for me was to mow often, and mow high. My four day streak was preceded by about 4-5 days of rest. The grass didn't really have a chance to get too tall. That kept me in the 1/3 rule. I sharpen my blade 2-3 times a year. That helps cut the wet grass instead of pulverizing it into a mush. I keep my mower set on the highest it will go. Dunno how high that is, never measured. Hope this helps.

Both of these "rules" are more like .... optimizations. 

With a manual mower, I would mow when it is wet instead of waiting.  Just because when stuff gets too tall, the mower doesn't cut as well. 

With the standard mower, I'd mow it wet if you A. have a sharp blade, and B. haven't waited too long. I think the mowing a wet lawn is a bit of a myth. I think what happens is most people don't keep their blades sharp. Then there is a rainy streak, which started on the day they should have mowed. They didn't mow so it got too long, and was still rainy and wet. This leads to a panic mow which cuts off too much (more than 1/2 the blade,) with soggy grass.  I can see that combo (dull blade, too long, wet) clogging the mower and shredding the grass instead of cutting it. Which I've been guilty of. Now I mow when it needs it, rain or shine. I've noticed the mower doesn't get clogged and matted up and the grass doesn't complain either. I agree with Paul that the reel mower is better. They clip the grass instead of taking a whack at it. A sharp blade on a standard definitely helps, but still doesn't approach that of a reel. If this mower breaks, I may be able to talk Katie into letting me buy one. Until then, I'll just make do with what I got. Besides, I like the exercise of pushing that heavy engine around.

This might be a good time to point out:  waiting is lazier.  Maybe I would go for waiting. 

Good point. Although when I wait, I tend to get overly enthusiastic in my waiting. Then the grass gets to the point where even on the highest setting it gets clogged, dry. There is a point when one can be too lazy. I for some reason abhor this point and tend to stay as far in either direction as possible.

Well I've been on all sides of this coin, including the edge! 

Where I'm at now is that I mow probably when it's too long and still a little moist if I have a window and don't see it getting any drier in the next day or two (taking the hopeful lazy until it's just too long).  When I get even lazier (and it gets longer) then that I'll switch to side discharge so I don't create grass mulch mats.

Rain's great, until it doesn't stop!

Tell me about it. My area is a clay pot, and my yard is the basin.