One of my friend's sons recently had a car accident. A very serious car accident. He was hospitalized overnight and did not return home. His live-in girlfriend was seemingly unconcerned that he was missing overnight, she didn't call him, she didn't call his friends or parents looking for him. After the car accident my friend's son broke up with the girl citing her indifference to his well-being on that particular night.
Better writers than I have written of friendship more eloquently than I ever could. But it all distills down to this: in your darkest hour, as the whirling waters around your head threaten to drown you -- who is the person you know is plotting for your rescue? Who is the person who may have taught you to tread water for just such an occasion? Who is sustaining you with bits of food and water? Who are the people who hear of your plight and come rushing to your aid? And just who is that one person who will jump in risking their own well-being to ensure that they will have done everything they can to save you, and that if you do go down both of you will go down together?
Alternatively, who is standing on the shore? Comfortably gazing from their position in repose? Laughing at the spectacle or criticizing the way you are treading water. Perhaps they avert their eyes to avoid their own discomfort or they've become bored with watching you struggle.
And once the crisis has passed you are armed with powerful knowledge. You know your own strength (and are significantly stronger than before the crisis). You have water treading skills that you can instill in others. And you know who your friends are....and who they aren't.