Great way to cause and accident.
Cars are equipped with turn signals and mirrors as standard equipment because they help make driving safer for everybody on the road. When drivers fail to use them, accidents can and will happen. Just take this BMW Z4 as an example.
While navigating and sitting in busy, bumper-to-bumper traffic, the BMW Z4 driver decided to live up to the stereotype of not using their mirrors and pull out into a lane with traffic flowing considerably faster.
The BMW Z4 quickly jumps into the faster lane from the bumper-to-bumper traffic only to have a Citroen DS 3 smash right into the rear/side of the sports car. The DS 3 spun into other lanes, got hit by a work van, and then slid right into the bumper-to-bumper traffic, hitting another vehicle as parts littered the motorway.
Had the BMW Z4 driver checked their mirrors properly and waited for an opening in traffic, none of this would have happened.
Check your freaking mirrors!
Source: Dash Cam Network YouTube