– The current tanda played by the DJ suits me.
– The girl with whom I’m wanting to dance is chatting with another girl.
– Another leader invites this other girl.
The first condition is easily met, almost anything but Di Sarli will do. The second condition is already much less frequently fulfilled; the lady tends to be in a larger group, or with a male. Same for the last condition, I have standard tastes so if a follower pleases me she will please the other leaders too.