As a kid I read that White had the advantage in open games (1.e4 e5) if he could get d2-d4 in successfully, so I wondered why he didn’t just play 2.Nf3 Nc6 3.d4 rather than mess about with the indirect 3.Bb5. After 3…exd4 4.Nxd4 I figured that White was threatening to give Black doubled pawns with 5.Nxc6 which Black should prevent with either 4…Nxd4 5.Qxd4 Qf6 or 4…Nge7.
Needless to say the opening theory of the time (the early 1970s) did not agree with my cogitations but it would turn out that I was not completely wrong. In his 1990 World Championship match against Anatoly Karpov, Garry Kasparov would use the Scotch to effect, and after 1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Nf6 played the Mieses Variation with 5.Nxc6 which inflicts pawn weaknesses.
Here is the 16th game in which Kasparov won in over 100 moves, quite a heavy psychological blow for Karpov:
Since this match the Scotch has had a new lease of life, with many other leading players having taken up White’s cause. It’s not just the Ruy Lopez that’s a problem White can slay him with the Scotch!