Not only do smartphones provide unprecedented access to information, they provide unprecedented opportunities to multitask. Any activity can be accompanied by music, selfies or social media updates. Of course, some people pick poor times to tweet or text, and lawmakers have stepped in. Forty-eight states have banned texting while driving. In Honolulu, it’s illegal to text or even look at your phone while crossing the street, and in the Netherlands they’ve banned texting while biking.

But legislation won’t proscribe all situations in which multitasking is unwise; you need to self-regulate. Understanding how the brain multitasks and why we find multitasking so appealing will help you gauge the hazard of pulling out your phone.

Multitasking feels like doing two things simultaneously, so it seems the danger lies in asking one mental process to do two incompatible things — for texting drivers, watching the screen and the road. A lot of lawmakers must think that way, because 20 states have instituted bans on driving using a hand-held phone while still allowing hands-free calls. Yet hands-free or hand-held makes no difference — they impair driving equivalently as far as external hazards go. Why?

You actually manipulate your phone only briefly for voice calls. The real problem is the toggling of attention between the conversation and the road. Even simple tasks can’t be done simultaneously; you switch between them, and that affects performance.