We take many of our driving cues from what is happening around us when we are in traffic. If we are paying attention and watching for the correct cues all goes well. Stop paying full attention to the driving task, accidentally take the wrong cues and you can easily cause a collision.
The case in point occurred yesterday afternoon. A car was waiting, first in line at a red light in the left hand through lane. I pulled up to stop beside it in the right hand through lane at the same time as the left turn signal we were facing changed to green. Signals for through traffic remained red as there were vehicles using the oncoming left turn lane.
The driver of the car probably saw the green light and my movement in the intended direction of travel in their peripheral vision and decided it was time to go. Something must not have seemed quite right because the driver did not accelerate as quickly as vehicles facing a new green light usually do.
Fortunately the oncoming driver was watching the right cues. He slowed enough that the driver that had been beside me did not collide with him, although it was a near miss. The driver beside me should have been watching the overhead signal for the lane that he was in. Once he saw the green he should have looked left, right and left again, to proceed through the intersection only if it was safe to do so.
Not paying full attention to the driving task and watching the wrong cues is an invitation to trouble. Add distractions or impairments to the mix and it becomes even more dangerous. The ability to focus yourself is an important driving skill.