MS2 here. This isn't a homework question, nor about a course or exam, so I hope it is okay. Sensitivity vs. specificity explanations have never made sense.

The way I understand it:

Sensitivity is used to rule OUT a disease. Sensitivity is best at correctly identifying the people WITH the disease.

Specificity is used to rule IN a disease. It is best at correctly identifying those WITHOUT the disease.

What is the actual difference between them? Imagine 100% sensitivity and specificity. The way I see it, sensitivity says, "You have this disease because you tested positive" or "You do not have this disease because you did not test positive." Then, specificity says, "You do not have this disease because you tested negative," or "You do have this disease because you did not test negative." Is this line of thinking correct?

If yes, then aren't they both good at simply confirming or denying disease? Is it that sensitivity tells us we can cross a disease off the DD because they did not test positive, and specificity tells us we've confirmed the diagnosis if they do test positive? Is it that we use higher sensitivity tests when we're narrowing down our DD, then a higher specificity test to confirm our suspicions?

I admit I feel embarrassed asking, but I really do want to get this down so I can fully understand test results when I am practicing.

Edit: thank you all for your responses! I received some really great information and analogies, also, confirmed that I do not like statistics.