I don't think we need to hold on to relief, to hold on to contentment when we come across it. As much as we'd like to, I think it's pretty clear from collective experience that it just doesn't work.
No, it's almost like a shift in the light, a scene that stops you in your tracks because it's suddenly illuminated. You're grateful for it. but too busy being struck by the unexpected revealing that it never occurs to you to want to hold onto it, to want anything for that matter. Instead, the light shifts, and you move on, lighter indeed for the chance revealing.