How do photographers manage multiple lenses?

This is probably a very naive question but I will ask anyway.

It appears that most photographers carry multiple lenses. Each lens serves a different purpose. I understand that. However, I can't understand how photographers manage to quickly switch lenses and still not miss any shots or damage the sensor. How would a photographer know what photo opportunity will present itself? I recently purchased 50mm 1.8, it is a fantastic lens for portraits but I do not just shoot portraits all the time. I may want to shoot a portrait of my kids on the beach at one moment, and then shoot a picture of them surfing far away next.

I understand that some pros shoot under very specific conditions: (sporting events, portraits) and they know exactly which lenses they will need. However, I have to assume that is not the case for most photographers.