Security and Stability - What Are the Unknown Costs?

If i know a major amendment is coming up, then i can estimate what the cost of the amendment would be and that would be in my budget. But there's costs that i don't know. So if the system, for example, they'd do an up date to the system, up grate its and break something else. Those are the unknown costs, and those are the costs that i try to avoid by going with more established companies or companies who have a tracke i make sense. And then you don't want to cost o security and stability.