Both through personal experience and academic research, it becomes evident that there are extensive prejudices against the development and existence of a bisexual identity. According to Rust (2000), "One of the greatest challenges facing bisexual women in contemporary Western culture is the belief that bisexuality does not exist. Women who claim to be bisexual are often told that they are 'denying' their true sexuality, which must be either lesbian or heterosexual." (Rust, 2000) Many straights and gays alike do not understand bisexuality, because they have not experienced it. Because gender is the primary qualifier for sexual attraction with them, they cannot imagine being attracted to either gender dependent primarily on other characteristics. Homosexuality itself may be easy to understand, because it is like heterosexuality in that it is sexual selection based on gender. Homosexuals may be envisioned as by hets as similar to heterosexuals of the other sex. Likewise, homosexuals can understand heterosexuality by empathizing with the opposite gender's feelings. But understanding a mindset where gender is not a major deciding factor may be incomprehensible. Thus bisexuals are seen as confused or in denial, merely because the observers themselves are confused by the bisexual state of mind. Moreover, this confusion leads to very negative stereotypes: "Images of the bisexual as promiscuous, needing multiple relationships in order to feel satisfied, untrustworthy in relationships, or as 'fence-sitters, traitors, cop-outs, closet cases,' reinforce the legitimacy of the heterosexual/homosexual binary and ensure the difficulty of publicly identifying as bisexual." (Mclean, 2001) It is a common misconception that just as monosexuals need at least one person of the desired gender to feel sexually complete, so bisexuals must need one person from each of the two desired genders to feel complete. This is an understandable confusion, but misleading in its implications. Because bisexuals are seen as especially promiscuous, they may be considered to be unfaithful and also more likely to spread diseases or immorality. Where many people of both binary orientations sometimes like to pretend that that homosexuals are "just the same" as heterosexuals accept with a different preferred gender, the idea of bisexuality conjures up visions of wild promiscuity which may not be justified.
Many authors blame this misunderstanding on history. For example, Kirsten McLean (2001) writes "Traditionally, Western society has divided sexuality into two categories -- homosexual and heterosexual." Such authors suggest that such a binary understanding of human sexuality was the norm until recently. Actually, nothing could be farther from the truth. Until very recently with the introduction of the idea of homosexuality, the norm for sexual deviancy was bisexuality. That is to say that people engaging in homosexuality were assumed to go both ways unless they were particularly unusual. For example, it is common knowledge that in the old Greco-Roman world "homosexuality" was the norm.