“Yeah, people have a tendency to be unsatisfied with how much they make, no matter what their income is.”

Your friend just told you a story about a former college friend who's quite wealthy but still doesn't feel like she makes enough money. You want to show that you understood the meaning of your friend's story. You say this, summarizing in a more general way.

Yeah, people have a tendency to be unsatisfied with how much they make, no matter what their income is.

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Yeah

"Yeah" is a more casual way of saying "yes". 

Say this to agree with something that a person said:

Yeah, no problem.

Yeah, I actually did it myself.

You can also say "yeah" when you're going to disagree but you want to make your disagreement sound a little softer.

Yeah, but then it'll be blocking one of the outlets.

"Yeah" sounds less formal than "yes." 

people have a tendency to (do something)

Use this phrase to describe things that people often do, in a philosophical or scientific-sounding way:

People have a tendency to associate themselves with those who they share common interests and values with.

be unsatisfied with (something)

To be "unsatisfied with" something means to feel like you don't have enough.

no matter what (something) is

Use this phrase to explain something that is the same in every situation, and the circumstances don't matter (they're not important):

Ideally, you should get it done as quickly as possible, no matter what the deadline is.

In the example at top, "no matter what their income is" means that the person's income isn't important. People who are poor are unsatisfied, and rich people are also unsatisfied.

how much (someone) makes / income

"How much you make" and your "income" are basically the same thing. "Income" is a more technical-sounding word.

People usually try to income / using the same word for something many times in a conversation unless it's a really basic word or if you really want to emphasize an idea. Instead, we usually look for different words or phrases to explain the same idea.