Tip at a Hotel

The other day , i was in a hotel having dinner with my cousin .We had a very good dinner and as we were about to leave, my cousin became furious with me about the amount that i paid as a tip to the bearer.

My cousin was from the US and he claimed that it is a norm that people need to pay atleast 10 percent of the overall bill as tip.

I argued with him why does someone need to offer a tip? It is a service that the bearer provides to the customers of the hotel and rightly he is being payed by his employer i.e. the hotel.So why should i pay.The argument went on and later i asked him,do we get paid or tipped for completing a work in the office?

He was just dumb struck. I also stated that, if we were to tip the bearers on the grounds that he/she is doing a low end job, then we have to do it for people who clean the table or for that matter anyone who does low end jobs like servants at home or corporation cleaners who clean the road.Which i think is a fair argument? We do not see that happening.

I still could not understand his argument or the theory of paying tip for a work that somebody is rightfully paid for by his/her employer.

I am still searching for an answer to that question.