As a lake management consultant, and owner of a lake management company, I get to see, first hand, many mistakes by pond owners. The biggest one, by far, is "You don't know what you don't know."
Every one has great intentions. Build the best lake on the planet, or have a nice pond, pristine water, and soothing. Whatever the mission. Mistakes are often made because that landowner hasn't completely thought through their goals, and then have a good enough understanding of their resources (money, dirt, knowledge), and then how to put those things together with a well-designed plan. I can't tell you how many times I've looked at a leaky pond...because something wasn't taken care of during construction. People commonly go over-budget with construction and try to "make it up" by scrimping on their fish stocking plan. Habitat is a big one. People think about their top end fish, but not the forage fish which feed them. The majority of "mistakes" could be prevented with just a little bit more knowledge. But, the problem with that circles back to "we don't know what we don't know."
One thing I've learned during the last 4 decades of this stuff is that we never know enough (including me). But, with the resources available in today's world, knowledge should be the least of our worries.
