The Rice University Neologisms Database

The verb phrase ‘go for it.’ When this initialism is applied to the self, it connotes a lack of self-confidence or an intention to complete the action being referred to quickly. This initialism may also be used to encourage another person to ‘go for it,’ especially if they are expressing uncertainty. The meaning of ‘GFI’ seems to be slightly less earnest than ‘go for it,’ possibly because a more flippant attitude lessens the negative result if the action being attempted does not turn out as intended. Since the initialism has the same number of syllables as the original phrase, the formation of the neologism seems to relate more to the slight change in connotation than to the ease with which the term can be said.