The commonality is obviously stupidity but besides that, the real monitary cost is hard to measure.
Sure you can look at whatever your investment was and write it off versus gains in another year but its more than that, its what we call opportunity cost which is simply the next best alternative.
For example, say you sank $100,000 into one of the above investing disasters fifteen years ago. You would have missed out on fifteen years of growth at 'X%'. Assuming just a measily 2% would be $134,000 today. At 10%, you'd be missing $417,000 today, not just your original 100k.
So when looking at investments, keep the lost opportunity cost in mind.
Remember that successful investing has as much to do with not losing money as making money and remind yourself that as a boomer, you do not have the time to make up from bad investments.