Let's take an extreme example.
There are a thousand white or black balls in a closed box.
I have to estimate how many balls are white.
I can make an additional assumption: all balls are white or all balls are black
I take one ball and it happens to be white. I put the ball back into the box.
(of course I cannot see the colour of the balls inside the box)
I can be 100 sure that the number or white balls is exactly 1000.
If you don't understand the example or you can't see the relation to my Spanish post, please retake Statistics 101.
Find me one Statistics lecturer who says that you can conduce a decent statistical analysis based on one observation.
Any first lecture on estimation will include some examples with a sample of only one element, or even zero elements.
Do you know that you can estimate a value with no sample?