People often say, "Why should I have to tip my server? That's their job, they're already getting paid for this," or, "Anyone can be a server, why should I tip them for doing something that anyone else could do?"
I can tell you firsthand that being a waitress in a busy restaurant is genuinely hard work. Managing your full section of tables who are all on different courses of their meals, while refilling drinks and making coffees, taking appetizer orders on one table before rushing to grab a dessert order on another table before needing to run drinks to a third table so that you're ready in time to sing 'happy birthday' to a fourth table before their desserts start melting in the kitchen window, all while getting triple-sat is quite a stressor.
Being a server really isn't for everyone. In fact, many people who are servers, should not be servers. It requires the ability to multitask in a fast-paced environment all while acting as a liaison between the clients and the kitchen. We have to deal with complaints from customers and mistakes by the kitchen, all while doing our best not to make any mistakes of our own.
I have been to many restaurants where servers provide wonderful service, are very attentive, and are overall very friendly and care about their job. I have also been to restaurants where the service was awful, and servers couldn't care less about their tables to the point where they would give an attitude when a client asks for some extra salad dressing. In having experiences like both of these, I do believe that the amount or percentage that a client leaves their server should be based on the level of satisfaction that the server provided with the guests. Not every server provides 20% tip service all the time.
However, our hourly wages are significantly lower than minimum wage because we are considered tipped employees, and so if you are satisfied with the service you received during your restaurant experience, your tip should reflect that. Basically, the income of servers is based about 90% on those tips.
On top of all of this, there are many, many picky and difficult customers. Requesting seven modifications or basically creating your own dish gives the server a lot more work because they have to relay it to the kitchen, which is a whole other process. Some customers like their Absolut martinis "extra extra extra dirty" with four olives, while their friend wants a Tito's martini only slightly dirty with three olives and a twist of lime. Then you have customers who are allergic to the world, others who are gluten free but assume that you just somehow magically know that they're gluten free by looking at them so that when their food comes out and it isn't gluten free, you're enemy number one.
Working in a restaurant really is hard work, and if you don't want to tip, either get take-out or eat at home, because while you're sitting in a restaurant knowing you won't tip your server, you are taking up a table and the time of a server who could be taking care of clients that would be tipping the server for all of their hard work.