The Drowning Child
Good, that response shows you’re clearly the sensible type.
Let’s recap what’s going on here. You have come across a small child who having gotten into difficulty in a shallow pond is crying in distress and possibly at risk of drowning. You have accepted you have a moral obligation to rescue the child even though by doing so you will muddy your clothes. The issue we’re now looking at is whether your obligation to help might be cancelled in particular circumstances.
A Degree of Uncertainty
Let’s imagine that there is some uncertainty attached to the situation. You know you’re not going to come to any harm if you attempt the rescue, but you can’t be sure that your efforts will make any difference to how things turn out. This is partly for the counterfactual reason that if you don’t intervene, then it is possible that somebody else will do so, thereby bringing about the same result (i.e., the rescue of the child from the pond); and it is partly because it is possible that by the time you reach the child, it will already be too late.
It is important to be clear about the precise situation here. You have good reason to suppose that your intervention will bring about a better outcome than would otherwise be the case, but you can’t be sure about it . The question is - does this element of uncertainty mean you’re no longer obliged to go ahead with the rescue attempt?
I am still morally obliged to attempt the rescue
This element of uncertainty means I’m not morally obliged to attempt the rescue