I must add - it doesn't always work. In fact it mostly doesn't but it's whatever to me.Depends on my mood.
If i'm talking to a girl that responds sporadically, we aint saying nothing deep anyway. Mostly check up shyt, some banter. What i'm really doing is measuring when it's a good time to call. When the frequency picks up a bit, then I call a bit later.
If i think she's bad, i'll holla her again at some point and see what it do. I've converted from these situations before but I consider it 10%/20% likely to happen. More leg work goes into girls that seem more interested.
A bigger thing for me is dates. Once I meet with a girl, the direction becomes more obvious. If I have a date with her and she's not interested in a follow-up soon, I know it's a write-off. Because if I can get a girl out on a date, there's a 70% chance we'll fukk.