Without the capacity for distraction, you wouldn't hear the taxicab horn when you step off the curb
Its within these situations, where multi-tasking would be moreover accepted. If you are following one task, whether it be checking your phone, and walking then you would not be able to scan your surroundings. If you were able to split your attention in between both, however, you would not be blind to your surroundings. Your senses would be more alert than to they would have been if you only focused on your phone. That being said, its not safe to be distracted on non-important tasks. When you're outside being a pedestrian, the only task you should have is being aware of your surroundings. Crossing busy streets or walking out onto the rode with no awareness of your surroundings can be fatal, especially if you were distracted by something else.