We must act.

We have no right to shut our eyes to knowledge which ought to guide our action because we are aware that action taken on that one factor will be insufficiently guided.

The one factor is an important one and must influence our action, and would influence our action if we knew all the other factors.

We ought to allow it to influence our action even in ignorance of the other factors.
In daily life we habitually act on partial knowledge, and we should think that man mad who urged us to refuse to be guided by our partial knowledge until our knowledge was complete; we should think a man mad who, being under necessity to act, refused to know what he could know, because he was aware that fuller knowledge might lead him to modify his action.

Now missionaries and missionary societies are acting and must act, and the refusal to collect the information which they can obtain is as culpable as the ignorance of a man who refuses to attend to the one word "poison" printed on the label of a bottle which he can read, because he cannot read the name of the stuff written on the label.
Yet it is very commonly argued that unless survey can be made complete, unless, that is, every factor which we can think of as exercising an influence on our action is duly weighed, it is futile to survey the larger, commoner, and more easily accessible factors.