“Data from questionnaire studies (Rombouts, 1987) suggest that [falling in love] is triggered by a specific sequence of events, in which the qualities of the love-object are of minor importance. A person is ready to fall in love because of one of a number of reasons – loneliness, sexual need, dissatisfaction, or need or variety. A object then incites interest, again for one of a number of reasons, such as novelty, attractiveness, or mere proximity. Then give the person a moment of promise, a brief response from the object that suggests interest. It may be a confidence; it may be a single glance, such as a young girl may think she received from a pop star. The give the person a brief lapse of time – anywhere between half an hour or half a day, the self-report suggests – during which fantasies can develop. After that sequence, no more than a single confirmation, real or imagined is needed to precipitate falling in love.”
– Nico H. Frijda, University of Amsterdam, The Netherlands in his paper on The Laws of Emotion.