Many matches are decided in the rallies. The Larry Line (can I copyright that?) is that level of speed, quickness, and spin (done consistently) that overwhelms a given opponent so that they start to either fall apart or are forced to back up and play defensively. Everyone has such a line; if you can find your opponent's and are able to play just above that Line, the opponent will become erratic or be forced to play defensively. The key here is not over-playing by going so far above this Line that you lose consistency. If you play just below it, then the opponent will feel comfortable and won't make many mistakes. Play 1% above it and your opponent will start to miss or make weak returns that you can put away.
Here's the corollary - if, instead, your opponent is able to find your Larry Line and you are unable to play above his, then you have to develop alternate tactics. Sometimes you can win because the opponent overplays, going well above your Line, and so makes too many mistakes. (Or, if they are a weaker player, they simply lack consistency whether above or below your Line.) Otherwise, either you play more defensive (usually stepping back to give yourself more time to react), or dominate with serve and receive, with early attacks that end the point before getting into too many losing rallies. But then, once the match is over, go practice to raise your Larry Line - because, if you are like me, you draw the line at losing!