My experience is that if a girl is interested or neutral then I have to act quickly, always. If I wait for too long, she will lose interest for ever, always. That's similar to what Mark Manson states in Models.

Nevertheless, every now and then I hear the story about people who got in a relationship or hooked up some months or even years after knowing each other, and even regularly doing things together. For example, they get to see each other for a year as friends as part of a club or a group of friends, or they have been work colleagues since long and then date each other.

How does that work? How come there is no issue with the friendzone nor dead interest over such a long period of time?