Why did general lee fail during his last stand at the appomattox court house?

On April 1, 1865, Major General Philip Sheridan's cavalry overflowed Lee's flank at the Battle of Five Forks. The next day, Grant's army made a decisive breakthrough marking the end of the siege of Petersburg. Lee left Petersburg and Richmond and went west towards Appomattox Station, where a train loaded with provisions awaited him. From there, he hoped to move south to join General Joseph E. Johnston's army in North Carolina. On April 8, 1865, Union cavalry commanded by Brigadier-General George Armstrong Custer captured and burned three supply trains awaiting Lee's army at the Battle of Appomattox Station. From then on, the Potomac Army and the James Army converged on Appomattox. The signing of the surrender documents occurred in the living room of the house owned by Wilmer McLean on the afternoon of April 9th. On April 12, 1865, a formal ceremony marked the dismemberment of the Northern Virginia Army and the parole of its leaders and men, effectively ending the American Civil War.