Protect the e4 square!!!

Controlling the center is essential, yet it's surprising how many people leave such a vital square like e4 unprotected.  If the knight gets to e4 the result can be disasterous for the other player.  In this game my opponent concentrated on developing a strong line of pawns without developing any pieces.  I saw the hole on the board and set my knight to attack.  My opponent hung in there for awhile but after 12 checks, white had had enough and quit ... what's two more checks?  I'm irritated that I had so many checks but this is still a beautiful game.  Constructive criticism is appreciated.  Thx.