Why dont people tip?

Assuming the following:

=Great Service
=Great product (whether restaurant service, spa treatment, hair cut, or anything where the server generally gets tipped)...
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You can answer this question freely if you are one of the people who don't tip considering this is the internet, and I will never "hunt you down" and yell to the world that "you don't tip".. .

but what is it?
I always go into a spa with the expectation that my bill will be between 15 to 20% more than what the service cost is...

so why don't others factor that in?
Are they so cheap? Is the money so important to them?
are they not greatful?

I always tip, unless my service was so bad that I had to complain - but that hasn't happened often at all.

I think it's a nice, useful way to show your gratitude to someone who has done something for you, even though they are getting paid for it. Some people might say, "It's their job, why do they need even more money for it?" and I say that it's because they didn't HAVE to do any little extras, they didn't HAVE to be so nice, they didn't HAVE to get your order right on the first try....anyone get where I'm coming from?

People who do their job and make you feel good while they are doing it are important, and we need them. I like to let them know that by tipping - and the odd arrangement of flowers, if they did something really special for me.

Appreciating people never gets tired.

I always tip. Even when service is bad. My work depends on tips. Few do not tip at all in my line of work. Several tip poorly but at least tip something.

Many people who do not tip fail to know they should. Everyone knows to tip after you eat. They fail to know to tip at motels, subway,dunkin doughnuts,drivers etc.

I don't think they are cheap they lack knowledge

Some people who use the services w/o tipping most of the time think of you as beneath them because of your occupation and your suppose to serve them, some elderly individuals justt don't believe in leaving tips, Some people are jus stingy and think that you already receive a paycheck from the company and that your doing your job, but different strokes for different folks there is no definite answer as to why tho'!

perhaps it is because everything is so dang expensive to begin with!
These days we can barely afford the goods, let alone tip on top of it.
I think they should re-vamp the pay scale for servers in restaurants and pay them what they deserve so we're not required to tip. It's old, out-dated, dumb. Just have their employers pay them what they should be making, for pete's sake!

B/C people are cheapskates...although, you know the U.S. is one of few countries around the world where it's customary to tip...so people from other countries just may not be used to it and may think it's absurd if they come from a country where people don't tip.

if you dont tip then you deserve to have a waiter spit in your food.

b/c they are cheap a** losers.

i don't know....i always tip