I've been doing a lot of streaming on a live-broadcast app called Periscope over the last several months. When people comment on Periscope, the comments quickly evaporate, even quicker when there are other comments pushing the previous ones out of the way. Fortunately, I can read and talk fast, so I catch most of them.
Opportunities are like Periscope comments. The slower you are to react, the quicker opportunities disappear. And like Periscope, there's no rewinding.
The difference with opportunities, though, is that they're not gone forever -- well for you they are -- they just go to the person who didn't hesitate or move too slowly.