These three aspects are: shutter speed, aperture size and sensor sensitivity (also known as ISO)

The notion that ISO changes sensor sensitivity, while true for film cameras (hey, each frame of film is a new sensor) is very much NOT for digital cameras — with the exception of a very few high-end cameras that have dual-sensitivity sensors.

For a lot of cameras, ISO is just a gamma adjustment done as the info is read off the sensor (e.g. Nikon, Sony). Camera behavior can be misleading because the auto modes (speed, aperture) use the ISO setting plus scene brightness to calculate the other settings. Misleading because DSLRs were first designed for film shooters.

Why does this matter? Well, if you crank up ISO in a dark scene and there are some lighter areas then a high ISO gamma adjustment can likely blow out those lighter areas as they are read off the sensor (i.e. before the data is stored as a raw or processed into a jpg). Much better to shoot raw mode in the dark — with a relatively low ISO and as long an exposure and as wide an aperture that you can stand. Now, in post, you can bring up the gamma selectively for the different ranges. In the shot below I did exactly this. (something I would not have been able to do with even fast film)

I’m mentioning this because “ISO changes sensor sensitivity” was something I thought was true — but it’s not.

Sounds like you started in film — yeah, me, too. Mostly Velvia transparencies. I still like that ‘look’ (obvious from the shot above).

Bright side: you can still teach an exposure triangle, but it’s Speed, Aperture, and Scene Brightness (i.e. available light — it really is all about the light).