The difference between knowledge and skill
Two very different things, any noob can be knowledgeable and know exactly what they are supposed to do, but in match, they simply won't do this stuff. It's because they are not focused enough really. I fall into this category, along with most everyone else.
You can not force it, you just have to ease strategies into your style. As you become more advanced you will notice that you start playing differently vs different characters. A noob version of this is samus vs fox. Samus missile cancels, and follows the missile hoping for a shine, which means a free downair. Other then that, there is not much of a difference in the way that samus would play vs a marth or the fox. However a pro, uses completely different moves, almost like a different move set, different mindgames, pretty much everything is different.
However, knowledge based, they might both be on the same level. They both probably know what they are supposed to do in certain match ups, but only one of them can apply it.
A good example of this is M2K. He has been probably the most knowledgable smasher since he started, but only recently (2006 I believe), he started placing high in large tournament.