Increased optimism in the face of a strong market jolt downward means that the pros and their friends spent or caused to be spent every bit of cash they could. This leaves no future demand to push stocks up. Before we get to the bottom, all that optimism will have been replaced if not by extreme pessimism, at least by what we had before last year's shift to increased optimism began. That must happen before the bottom is reached. As stocks fell in February, March and early April, sentiment did deteriorate, as you might have expected, but not nearly enough.
Sentiment is still more bullish than it was last summer.
To erode that and to really hit the bottom, quite a bit more mayhem must ensue. En route there will also be some short, sharp upward moves. These are just corrections to this bear market and temporary. Don't let them fool you. It remains a time to be maximally defensive.