The Art of Photography is the Art of Compromise.
The human eye is always moving, changing focus and sensitivity continuously as it takes millions of snapshots of a scene in a second. Our brains integrate these images into one continuous impression of the view. The photographer must approximate this complex activity by recording a single image, usually in a fraction of a second.
To get “everything” in focus at once (a large depth of field), the camera lens can be set to a small opening (a high “f-stop number”). But little light gets through a small hole, so the shutter must be open for a long time. If the wind moves something during that time… it will be out of focus. If the camera moves… the whole scene will be out of focus.
To increase the shutter-speed one can “open” the lens (use a smaller “f-stop-number”). Now, only part of the scene will be in focus.
One can use the same shutter speed and increase the sensitivity of the detector (use a higher “film speed” or ISO number). But this increases the graininess of the film image or the electronic “noise” in the digital detector. So a tiny image may appear clear but an enlarged picture will look blurry.
Photographers often envy painters, who can choose to leave things like power lines and other distractions out of scenes. The camera records what is there, whether we want it to or not. Small imperfections can be removed using a digital photo-editing program, but the constant challenge is to record accurately just what we want the viewer to see, and display it as a true reproduction of that “moment in time”.
If you want a close-up picture, you can chose to use a telephoto lens and stand away from the target. But a telephoto lens has a dimmer image than a regular lens and has a smaller depth of field for a given opening (f-stop setting). So the shutter speed must be slower, and the telephoto also magnifies any motion of the camera that occurs when the shutter is pressed.
You can use a normal lens, stand far away and enlarge the image later. But once you start to enlarge the image, the graininess of the film/detector starts to make the image look blurry. Your best option is to use a normal lens and get as close as possible. The closer a lens is to the target image, the smaller the depth of field becomes. So one must maximize the depth of field by using a small opening (high f-stop number)
…… see "get everything in focus" above.