If I am making a change to long method I can understand what this method is doing. I am more likely to take care in making changes because I can see the potential problems and I have a visual indication of the complexity of the code. Also I might be less likely to make changes unless necessary because of the complexity.
When working on a shorter method, changes are easier to make and the context and complexity are hidden. The side effects of the changes are harder to see, so I am more likely to make a change which can break things and not know that it will cause problems.
Unit testing should provide a measure of protection against this kind of problem (side effects of changes). The actual experience of writing, updating, and running the tests adds its own complexity, though, so I'd view them as a big help, but not an easy to apply solution.
When working on a shorter method, changes are easier to make and the context and complexity are hidden. The side effects of the changes are harder to see, so I am more likely to make a change which can break things and not know that it will cause problems.