And it is. And you press it home.
Thinking for sure that you'd lost it, you breathe a little easier.
And then, your breath catches in your throat. That one piece, put into its proper place, makes the overall image clearer than you could have imagined...
Another portal to the past opened. Such time travel has been known to you since the beginning. Since that time when a large-enough accretion of your sensory experiences allowed you to think for the first time, Here I am...
Before that, there was the laying of the foundation. Try as you will to see into that period of the past, it remains hidden from view.
Here I am.
But, who are YOU?
"...According to this line of criticism, the sense of self is an evolutionary artifact, which saves time in the circumstances it evolved for. But sense of self breaks down when considering some events such as memory loss, split personality disorder, brain damage, brainwashing, and various thought experiments. When presented with imperfections in the intuitive sense of self and the consequences to this concept which rely on the strict concept of self, a tendency to mend the concept occurs, possibly because of cognitive dissonance." [source]
Looking back down at the puzzle, you become aware of another missing key piece. The collection of unplaced pieces seems to have grown, and somehow you're almost convinced that that key piece isn't to be found within it. Maybe the cat ran off with it...
Is there any lemonade left in the fridge?