Aw heck. If a girl likes you, maybe she's seeing things in you that you have trouble seeing yourself. Perspective, you know.
Of course, if you really believe what you say, then it probably is as you describe, self-fulfilling prophecy. There's a book by Richard Bach called Illusions that has some great one-liners in it, including "Argue for your limitations, and sure enough, they're yours."
This thread reminds me of a famous saying of Groucho Marx. The following is from a site called Wikiquote:
"PLEASE ACCEPT MY RESIGNATION. I DON'T WANT TO BELONG TO ANY CLUB THAT WILL ACCEPT PEOPLE LIKE ME AS A MEMBER."
Telegram to the Friar's Club of Beverly Hills to which he belonged, as recounted in Groucho and Me (1959), p. 321
[Variant:] "Please accept my resignation. I don’t care to belong to any club that will have me as a member".
As quoted in The Groucho Letters (1967) by Arthur Sheekman. The sentiment predates Marx by 61 years, however; it likely originated with John Galsworthy in The Forsyte Saga. In Part I, Chapter II, "Old Jolyon Goes to the Opera", it's said of Old Jolyon that, "He naturally despised the Club that did take him." after another refused him because he was in a trade.
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"When you ride over sharps, you get flats!"--The Bicycling Guitarist, May 13, 2008