She's standing by the bus stop, why should I talk to her? Why not?

The group is heading to lunch, why should I introduce myself? Why not?

Really cute girl is walking out of class, why should I stop her and start a conversation? Why not?

You guys get the idea, and yeah feel free to subsitute any situation where you might have asked yourself "why do this?"

If you ever need to ask yourself "why" and cannot come up with a reason, you're doing it wrong. Because at that exact moment you could be asking "why not" and you still would not have a reason. Whatever anxiety might keep you from social interactions, not just seduction, prelude your thoughts not with "why" but with "why not."