It is White’s turn four moves into the Four Knights opening. He is considering Bc4 to develop his pieces further. What happens if he plays that move? Picture it: his bishop and e4 pawn will be in the classic position to be forked by Black’s d-pawn, and Black would be able to replace the pawn on e4 with a suitable target by playing Nxe4, inviting the reply NxN. Now White’s knight and bishop would be forkable with d7-d5. True, White could then take Black’s pawn with his bishop (Bxd5), but then Black plays QxB. When the smoke clears, Black will have won no material but will have a better position: a pawn in the center and both bishops ready to move. The point of the position is not the precise outcome, though; it is the importance of hesitating before leaving one of your pieces one square away from any of your own pieces or pawns on the same rank. Consider whether your opponent could start an exchange that would create a working pawn fork at the end.