The answer to 'what causes shut-off valve' is that a shut-off valve can become stuck or difficult to turn for a few common reasons. Over time, the valve mechanism can become corroded or mineral deposits can build up, preventing the valve from opening and closing properly. Excessive force or improper use when turning the valve can also damage the internal components and cause the valve to malfunction.
In some cases, the valve may simply be old and worn out, especially if it's an original valve that's been in place for many years. Valves can also get stuck if they haven't been used in a long time. Regular use and maintenance is important to keep shut-off valves working smoothly.