Rob is a fairly simple man, but very introspective; he is prone to going off on mental tangents and equating everything in his life with everything else. Because of his relative bad luck in romance, he thinks a lot about the differences between men and women -- and he doesn't always get it right. Especially at the beginning; he is obsessed with finding out what is wrong in his failed relationship, and cares little for the idea that women have as many standards -- and personal flaws -- as he does, and as all men do.

...proper men, the sort of men that women have in mind when they moan about us. It's a safe, solid, meaningless stereotype: the man who... gets ditched and maybe sits in the pub... and then gets on with things.

[...]

...the chief attraction of the opposite sex for all of us... we need someone... who can stop us from falling down into the pit where the permanently single live....
(Hornby, High Fidelity, Google Books)

For a time, Rob thinks that all the difference is in the essential romanticism of a relationship, the romance that he believes exists more for men in their youth and then more for women in their adulthood. If young men want a fiery romance, older men can't understand why their efforts become ignored. Rob eventually learns that flawed humans, men and women, cannot have an ideal of romance or love, but instead can have a comfort of each other. They might not always understand each other, but they are happy instead and sometimes that is enough.