[umvi]

Some people are very timid at things like left turns and roundabout entry because they are not confident in their judgment of oncoming car speed, etc. (mostly Americans on that second one; Europeans seem generally seem comfortable entering roundabouts).

[vkjv]

They may also be uncertain what another driver will do. For example, turning right onto a two lane road may be safe if the right lane is open. However, despite it not being legal, a driver in the left lane may change lanes mid intersection. I'd prefer not to risk it to save myself a few seconds.