I'm curious about something I've read on the Code of Canon Law. It reads that a vow isn't valid if you don't "possess suitable use of reason" to make it. So, I understand that you can't make a vow while drunk or something like that, but I'm not sure to what other situations this would apply.
If a drug addict, while not under influence, were to vow to never use drugs again, knowing that it is very unlikely, would the vow be valid? You could argue that the person isn't being reasonable, but at the same time they knew that they were likely to break a vow like this and vowed anyway.
What if someone vows to pray 10 rosaries every day for a month, but immediately thinks twice and regrets it, would it still be valid? I understand that, if the person were to regret it in a few days because they were struggling to keep it, they would need to talk to a priest to be released from it. But does regretting it immediately imply that the person wasn't thinking clearly when making the vow?