Mate, The old European tracks it is VERY hard to pass another F1 car.
Think about this, he over took Jenson and 2 BMW's in 1 chicane (major risk) but never had a CLEAR oppitunity to pass Alonso.
If you have never raced it is hard to think thats its hard to pass, looks easy on tv and seems easy in theory but really its not.
Even in Karting for me its a pain in the ass.
Senna was great at qualifying, but again he had a terrific car under him too.