As long as you're not in the spacefaring, automotive, banking/insurance, and medical industries, it's probably the case that it's acceptable to have some downti

As long as you're not in the spacefaring, automotive, banking/insurance, and medical industries, it's probably the case that it's acceptable to have some downtime and bugs - nobody will die or have their livelihood destroyed by it. Given this, your confidence threshold for a release is not approaching 100%, it's hitting some "good enough" value, where the work you're doing to test for the next 1% is 2x of the testing you're doing now and is "not worth it". As you burn through some sort of error/downtime budget, you'll adjust that level of confidence - as you have more problems, and take more time with responding to problems. Continuous deployment's upside is a confidence in the release process (since you do it so often), and some assurance that you'll be able to find the problem reasonably fast (since you only have to look through a smaller number of changes). You'll have fewer bigger problems, and more smaller problems. There definitely are cases where 10 smaller downtimes of 5 minutes is worse than 1 larger downtime of one hour, but usually it's better to have the former.