One of the joys of watching good clay-court tennis players such as Rafael Nadal is seeing them get to balls that seem to be unreachable. Strong clay-courters never stop running for shots. While the pros are in better shape than most recreational players, running down balls relentlessly is a simple way to assert yourself in a match regardless of the surface. If you make yourself try for every shot you will:
Retrieve shots you thought were out of reach: Many recreational players underestimate their ability to run down difficult shots; they stop trying even though they might have a chance to return the ball. This is a skill that improves over time; the more you practice it, the better you'll get.
Pressure your opponent: If your opponent knows that you're going to run for every ball you may force him to attempt difficult shots in an effort to shorten the point. And this will often draw errors. Retrieve well enough and you might even begin to get into his head and break his game down, just as Nadal did to Roger Federer in the 2006 Roland Garros final by doggedly chasing down everything, causing Federer to go for more than he could reliably produce.