This is another version of tip of the day because so many tips come from a lesson learned the hard way, but I thought this might be a more amusing topic- and just as useful.
My bonehead play of the day was to not put a tarp or landscape fabric down before having 10 yards of expensive shredded wood mulch dumped on a site with well established bind weed. Two weeks after the delivery and bind weed has already passed through a 3 ft layer of mulch. Seems like it may need to be treated with roundup, but I will try repeated pulling first.
Bindweed is truly the weed from hell in our region. It's the reason I use a lot of woven landscape fabric in my veg garden, even though I don't like plastic there.