4. Sony's Memory LapseSony's ( SNE) massive earnings revision this week had us reminiscing about the days when the Walkman maker ruled the earth. Sadly, it also reminded us how far the Japanese giant has subsequently stumbled. So as a tribute to the once-proud PlayStation maker, let's play a little 5 Dumbest memory game, shall we? First, think back to February -- yep, we know it's a long, long time ago but please play along -- when our good buddies at Sony projected an annual loss of 220 billion yen, or $2.7 billion, mostly due to feeble TV sales and the flood in Thailand. Next, while keeping those figures in mind, fast forward to this past Tuesday when Sony said its annual loss would actually be 520 billion yen ($6.4 billion), as a result of a massive tax charge. Now compare the two numbers. Do you get a 300 billion yen difference in barely 2 months like we do? Excellent! That wasn't so tough, was it? Simple math, and simple short-term stupidity. Nothing new for Sony. The next question revolves around years, not months, of ineptitude, so it may be a little tougher on the old noggin. Here we go: In what year did Sony last turn a profit? The answer is 2008, when it posted net income of 369.4 billion yen. Including this week's 520 billion yen loss, Sony has bled 919.3 billion yen in red ink over the past four years. Alright, for the last one let's really stretch those brain cells and go back over a decade of dumbness at Sony. After Tuesday's 9% sell-off, the company's market cap stood at $18.3 billion. How much was the company worth in 2002? Check this out: In March 2002 Sony's market value stood at $42.4 billion, more than double its current level. And as you may or may not recall, that was down by two-thirds from its March 2000 peak of more than $125 billion. Meanwhile, Sony's rival Apple ( AAPL) has seen its market value grow from $8.3 billion ten years ago to almost $600 billion this past week. We wouldn't mention that last fact to Sony CEO Kazuo Hirai however. We have a feeling he'd rather forget it.