𝐋𝐎𝐎𝐊 𝐁𝐎𝐓𝐇 𝐖𝐀𝐘𝐒 ˢᵇᵍ

Because traffic may be approaching from either direction. It's a good idea to look both ways before even entering a one-way street, you never know if there might be a wrong-way driver or especially a pedestrian or cyclist approaching. Children are taught to LOOK BOTH WAYS before crossing any street, always.