Every nice shot feels like a lucky shot... especially in Street Photography, where it is extremely difficult to foresee a specific situation (although I read some shot stories where the photographer really had a specific image in mind an waited hours for the scene to happen!).
For this specific one, I was idling around in the MOMA in Tokyo, half looking at the paintings and half looking a the people looking at the paintings, camera on and ready. The X100s allows for customized settings, so I could stay in full auto mode, knowing the camera won't decrease shutter speed below 1/40th and won't increase ISO too high.
I saw the scene from the far end of the corridor and had to rush closer to catch it, even with the TCL converter already attached and giving an extra reach (50mm full-frame equivalent). But should I have needed to change any setting, the scene would have disappeared, as the two men in the picture moved just a second later.
The picture was shot in RAW and converted in LR5.4 later, by adding a bit more contrast and slight vignetting.
Lessons learned: keep the camera ready, with settings matching the conditions and don't hesitate to rush to catch a specific image! if you feel it's a potential good one, trust your intuition!