One of the most difficult issues security managers have is justifying how they spend their limited budgets. Calculating a return on investment for a security countermeasure is extremely difficult as you rarely have the ability to calculate the savings from the losses you prevented. However, if you start to consider that Security is actually Risk Management, you can start determining the best countermeasures to proactively and cost effectively mitigate your losses. By determining the vulnerabilities that are most likely to create loss, you can then compare the potential losses against the cost of the countermeasure. This allows you to make an appropriate business decision as to justifying and allocating a security budget.
More importantly, if you can make such a business decision, you can justify increasing security budgets for additional countermeasures. The key is to be able to specifically identify an area of potential loss, and identify a security countermeasure that cost effectively mitigates that loss.