Truth – Anyone can take a decent picture these days. Fact – Not everyone can create portraits that evoke emotion. To be a good photographer you need to visualize the portrait in your mind and decide how you want it to look and feel before putting eye to the camera.
For example, if photographing a sporting event or whale watch the photographers goal might be to freeze the action and moment. To do this a high shutter speed like 1/1000th of a second is required. Depending on the light and ISO this means the F stop or depth of field can be maintained at around F8. Here is an example.
On a recent whale watch I observed a baby flicking its tale at the surface. I wanted a fast shutter to freeze the action but not so fast that the motion of water flowing off the tale was affected, so I chose a 1/800th of a second.

When creating landscape portraits Shutter speed can be used to slow everything down, which as a result creates emotion. For example when at the beach slowing the water flowing onto the sand or around reef or rocks creates a silky, foamy affect which exudes emotion. See the image below.

This image was created in the mid morning, when the light was already bright. I wanted to slow the water down to create wispy lines in the foreground but not slow it down so much that water crashing on the rocks in the background becoming too obscure. I selected a slow shutter of 1/15th of a second and F-22.
Had I selected a shutter speed of 1/500th or 1/1000th I would have frozen the spray in the background but the foreground would not have the silky trails.
With Aloha!