depends on the cameras tech… AF mostly uses phase detection (contrast), and is attuned to vertical lines. So… AF REALLY struggles with low contrast and horizontal lines. Manual focus is a must. Higher end cameras can use a more active focussing system or ‘cross type’ sensors that gets rid of the 'horizontal line probelem.

Trap focussing… eg shooting Formula 1, you want motion blur int he tires, maybe use the panning technique to blur the background a bit as well… you don’t want active AF on lower end cameras, so you manually focus in advance and shoot the car as it passes.

times where the foreground insist on locking your AF, but you want to actually be focuses well past it.

many lenses focus past infinity. If you a re shooting something unusual and the camera struggles to focus, pulling it backa tad can produce sharper result.

Hyperfocal point - Google it for details, but it is the sweet spot of a lens that gives the maximum depth of field for a focal length/aperture combo. It is a ‘virtual’ point in space you need to set manually. eg an object at 1meter… I want everything to infinity as sharp as possible, so my perfect hyperfocal distance may be to focus… 1.3m. (many older lenses had markings on the lens for this)

Something often forgotten… your focussing screen is not made for manual focus, it’s why it is seemingly impossible, especially if your eyepiece is not set to the right diopter for your eye. This is where in a typical DSLR you would look to change the screen (if it has that option) to a split screen, which is a manual focus aid, not unlike a rangefinder.

Best diopter adjustment method btw… remove your lens in a cleanish environment, then adjust it using whatever markings are on the screen. That way it’s more accurate and actualyl set to the screen. Doing it with the lens on is much harder

I’m old school (hence lots words to make a point lol), but gotta say… AF has indeed come a long way and can be relied up mostly. Especially in midtier to high end cameras with extras AF points that have the cross-type sensors and can work under lower light and smaller apertures. That said… a DSLR will never be able to focus as accurately as a decent rangefinder camera… and it shows to a trained eye. This has been repeatedly demonstrated in bench tests too. Take a DSLR and fous on an object 3 or 4 x, then do it witht he rangefinder… the DSLR will vary each time (slightly), whereas the rangefinder will consistently give the same result (in trained hands)

I hope that diatribe helps