For a 90% CI there is a 10% chance that the answer lies outside your estimate, and if you split this there is a 5% chance that the answer is above your upper bound and a 5% chance that the answer is below your lower bound.
This isn’t always true. For example, one calibration question I’ve done is, “How long are all 3 extended Lord of the Rings movies back to back?
On this, I was almost certain they were at least 3 hours long, but I wasn’t sure how much more than that they were. So, my minimum was 9 hours. I was fairly confident they weren’t more than 4 hours, so my upper was 12 (this was for a 70% interval). Almost all my uncertainty was on the upper end, while very little was on the lower.
This isn’t always true. For example, one calibration question I’ve done is, “How long are all 3 extended Lord of the Rings movies back to back?
On this, I was almost certain they were at least 3 hours long, but I wasn’t sure how much more than that they were. So, my minimum was 9 hours. I was fairly confident they weren’t more than 4 hours, so my upper was 12 (this was for a 70% interval). Almost all my uncertainty was on the upper end, while very little was on the lower.