A good portrait or candid photographer at a wedding, party or seminar will be in the right place at the right time and predicting events to take place.
A good product photographer is patient and meticulous setting backdrops, surfaces, screens, lighting and softboxes. He will think about using natural and/or flash lighting and the way things reflect in the most optimum way. A single successful product shot can easily take 2 hours to set up and light correctly.
A photographer understands depth of field, aperture settings, shutter speeds, bouncing flash, when to use a tripod and when not too, how to compensate for poor light, what he can and cant take for privacy or moral reasons. He will always be looking for that perfect shot.
Photography is about getting lucky with eyes being open, people smiing and objects or peole not appearing in the background.