Here is a simple rule I follow:

Rule 1 of 1: If I think "it" is the right thing to do, I do it.

Definition of "It": "It" refers to whatever action seems to exhibit the most of the following traits: the safest, most logical, simplest, most courteous or most selfless thing to do in the "situation".

Scenario: Narrow path, old lady walking her foofoo dog on leash. Bike rider is coming up behind lady with dog.

Options:
a) Do nothing and pass
b) Announce and pass
c) Go around

Correct response for me: in that situation is "c" go around. I would not want to startle the dog or the lady. Either "a" or "b" could have a bad outcome for the old lady.

Every situation is different. I make my mind up based on what I see and take in.