Ann: Change of Director's Interest Notice, page-67

SP bottoms are incredibly hard to pick. 1. People won't buy while SP is falling ("don't catch a falling knife"). 2. Stop-losses generate sells when SP is falling, so make SP fall further thus generating more stop-losses. 3. Bottom-feeders tend to buy passively, ie. let sellers pick up their low bids, so they don't push SP up. 4. Shorts get diminishing returns on a falling SP, and have to keep selling more to keep up the pace. All of this means that selling is self-reinforcing way past the notinal "fair value" point.
You could put it this way: Sentiment doesn't turn until the SP turns. SP doesn't turn until sentiment turns.
So - identify value then buy then wait patiently.