Knowing and proving are often two different things. One may know the law but may not be able to prove its relevance in a particular case. In the US, the prosecution has the burden of proof in a criminal or civil charge. All the criminal defense lawyer has to do is to disprove the evidence against the defendant, or to introduce reasonable doubt.
In jurisprudence, the reasonable doubt standard in the jury system is actually instructions to members of that jury that as reasonable people they must believe in the guilt of the defendant beyond a reasonable doubt. This may seem like a very vague and highly subjective standard, which is why in most cases brought before the jury or judge, it is important that the lawyer on either side is able to present their arguments persuasively and convincingly. It is not enough that the lawyer knows the law and how it applies to a case; the jury or the judge must understand and see it in the same way as well. This is not to say that lawyers have to deliberately mislead; rather, they need to be able to make the jury members or judge see the case from a particular perspective.
While perhaps not as dramatically portrayed as on television, in a real court case the bare facts of the case in point can take on a radically different meaning depending on how it is presented. The defense lawyer has to be able to find a plausible explanation for the facts as they appear to the advantage of the defendant. This is not to say that the prosecution’s interpretation of it is wrong; it merely suggests that another explanation is possible. And this introduces reasonable doubt. In a court case, it is important that the lawyer establishes a relationship with the client, the jury and the court officers in order to determine the right approach to a particular case. As pointed out by a co-counsel of Bryan Bleibdrey on the website of The Woodlands based BB Law Group PLLC, his interaction with the client and his cross examination of witnesses helped to prove the case in point.