Occam’s Razor (Wikipedia) is the principle that, all things being equal, the simplest solution tends to be the best one. Occam's Razor suggests how a case should be defended (as simply as possible -- see Scott Greenfield's "The KISS Principle” post prescribing a “surgical” approach to defending criminal cases); it also can help predict how successful a defense will be.
When you have a criminal case to defend, every piece of evidence will fall into one of three categories:
Things you contest (“no …”);
Things you explain (“yes, but …”); and
Things you accept (“so what?).
For example, an alleged witness says that she saw your client at the scene of the crime. You can contest this (challenging the witness’s credibility and presenting alibi witnesses to say, “No, he wasn’t”); you can explain it (“Yes, he was there, but not for the reasons the State supposes); or you can accept it (“Yes, he was there. So what?”).
Another example: the complaining witness in a murder case is dead of a gunshot wound. Perhaps you could contest it (showing that something else might have killed him before he was shot); you could explain it (“yes, but he killed himself”) or you could accept it (“Yes, he was shot to death. So what?”)
At its simplest, the defense of a criminal case involves only acceptance of the facts: “Yes, everything the witnesses said is true. But so what? That’s not proof beyond a reasonable doubt.” These cases come up often — usually because the State makes unwarranted assumptions about what the law requires. For example, Weed in the Car cases are often pure “so what?” cases.
Every contest and every explanation, however, complicates your case. Complicating your case is not desirable (per Occam’s Razor and Greenfield’s Hello Kitty Safety ScissorsKISS Principle). So we can amend the list. Now every piece of evidence falls into one of these three categories:
Things you have to contest;
Things you have to explain; and
Things you can accept.
Whether you have to contest or explain a circumstance depends on the facts of the case. Some things can never be accepted. For example, an “eyewitness’s” testimony that the accused committed the crime must be contested. The ultimate circumstance that requires explanation is the fact that the defendant has provided the government with a recorded confession. When the accused, informed of his right to remain silent, persists (against my Good Advice) in baring his soul to the police interrogator on videotape, that is a circumstance that can sometimes be contested (for example, by challenging its voluntariness) and rarely can be accepted; most often, though, the only course to take is to explain it (“here’s why the accused gave a false confession”).
In keeping with the “cutting implements” theme, then, here is Bennett’s Chainsaw:
The more things you must contest and the more explanations you must provide in order to mount a defense, the more likely it is that you will be convicted.