I can answer that. A lot of times, especially if the friend in question is opposite of gender 18 or older, they may have sex on the brain. And when that person hears from you that you just want to be friends, or in the other term, put into the Friend Zone, that person will feel like they failed at getting the sex they wanted, or Ever will from you. Also, that person may not fully understand or appreciate what truest Friendship means, without expecting something like sex in return in the first place. In these situations, they set themselves up for easy disappointment. Whereas beginning a new friendship without the sexual expectation and later on if you feel like exploring with this person, and you tell them that, they will generally feel more success, as the relationship is progressing from a more positive start point of genuine friendship. And going into said new friendship with low expectations, they will feel less disappointed in being Just Friends, as they would not have had the higher expectation, or that desire for that something in return, in the first place.
