Basing Decisions on Missing Information

Most often when faced with a decision, we want to gather as much data as possible in order to reach the best conclusions in our decision-making process. This much is perhaps rather obvious. But what do we do when there is missing data? It will then be tempting to discount whatever is missing as simply unavailable for the decision-making process, but perhaps we should be asking why the data is missing, and what we can learn from that fact.