REST vs SOAP, the difference between soap and rest

Someone asked me a question today “Why would anyone choose SOAP (Simple Object Access Protocol (http://en.wikipedia.org/wiki/SOAP)) instead of REST (Representational State Transfer (http://en.wikipedia.org/wiki/Representational_State_Transfer))?” My response: “The general rule of thumb I’ve always heard is ‘Unless you have a definitive reason to use SOAP use REST’”. He asked “what’s one reason?” I thought about it for a minute and honestly answered that I haven’t ever come across a reason. My background is building great internet companies.