I try to keep the waste I produce in check. I try not to generate any plastic trash, I take my lunch to work in reusable containers and try not to buy anything in a disposable cup.

I said, I try.

Truth be told, on my way to the office this morning I really needed a coffee. And yup, I picked up a hit of rich, dark, life-saving caffeine in a paper cup. In just a few sips, my carbon footprint was some 110 grams (nearly four ounces) heavier. And that's an extra weight on my conscience too.

I have to admit, for as long as I was drinking the coffee, I didn't feel too bad about my misdeed, but as soon as the cup was empty, it just stood on my desk, staring at me. "I knew you couldn't resist me," it seemed to be saying. Next to it, my beloved china mug was a picture of disappointment.

Every day we're faced with choices, with potential sacrifices and our feelings about how we impact the planet. But what determines the decisions we make?

"Everyone has to decide for themselves," says Gerhard Reese, an environmental psychologist at Germany's University of Koblenz-Landau. "It's a matter of social norms and our own moral codes."

From knowledge to action

Research suggests that as a 31-year-old German, I should find myself in a good company, because those in my age group are the biggest consumers of take-out coffee. At the same time, many people my age would probably say they're pretty environmentally aware.

That, however, really means not just knowing that climate change is happening, but being ready to do something about it. These days, it's pretty hard to fail on the first, but knowledge doesn't automatically lead to action – to preventing waste, saving water and energy, to buying less and choosing more sustainable products.

Most people responding to a recent German YouGov survey said they tried to do without plastic where possible, to repair things rather than replace them, and to use energy sparingly. But according to one study, around 460,000 coffee cups are slung in the trash every day in Berlin alone.

So why the disconnect? Why don't we do more?

Psychologists call it the intention-behavior gap, and it's something the relatively young discipline of environmental psychology is taking a close look at.

Bad habits are hard to kick

Experts say there are host of factors that contribute to our actions falling short.

"Of course, the routines we've acquired over many years of socialization is one reason," says Reese, who grew up in a two-car household. "It was just taken as a given that I'd get my driving license when I turned 18."

He says it's time to break such habits and expectations.

Read more: How hard is a low-carbon lifestyle? A Berlin family tells all

But people struggle to give things up, says Elke Weber, psychology professor and environment expert at Princeton University.

"Studies have shown that people feel the fear of losing something twice as much as the anticipation of gaining something."

Which means the positive impacts we could have on the planet if we change our behavior serve as less of a motivator that the loss of personal freedoms, such as driving a car.

And that, despite the regular stream of bad news relating to the environment.

From the oceans full of trash, the air pollution choking our cities, farmlands soaked with chemicals, ancient forests lost forever and species depletion to an ever-hotter climate that's fueling natural disasters across the planet, the stakes could hardly be higher. Yet many of us struggle to relate to this planetary emergency.

Read more: IPCC 1.5 C degree report points to high stakes of climate inaction

A problem happening elsewhere

"Climate change as a theoretical construct definitely has a few factors that make it hard for people to deal with," Reese says. For a start, it feels a long way off, in both space and time, as long as we don't experience dramatic effects first hand.

The solutions can also feel theoretical. People are reticent when they don't see immediate results from their actions, Weber says. The steps we take to protect the planet now will probably only have a concrete impact for future generations, "but the effort we have to make now is very real."

All of this means many of us just don't give our actions considered thought. "And not thinking obviously doesn't help," Weber says.

What does help though, she adds, are laws and political frameworks that encourage better behavior – like, for example, Germany's Renewable Energy Act, which encourages ordinary citizens to invest in green power by guaranteeing a fixed return on every kilowatt-hour produced by a rooftop solar panel. 

Reese says we also have a lot of influence over each other's behavior. "If I realize I know a lot of people who are vegetarian then I'll probably ask why," he says, "and maybe try it myself."

Small steps lead to something bigger

Anyway, back to my coffee cup.

Reese calls everyday decisions like these "behavioral cosmetics" – that, nevertheless, can add up to important change. What's more important though, are what he terms "big points": Reducing living space, not using a car and taking the train instead of flying abroad for vacations. 

But that doesn't excuse my slip-up this morning. Because the little "peanuts" play a role too. For one thing, they can lead to bigger change, according to the German Environment Agency (UBA), which says the idea that we should take the most important steps first doesn't mean we should talk down the contribution of consumer decisions.

Read more: Collective push against climate change more powerful than you'd think

The everyday practice of environmental awareness might not seem like much from a  global perspective. But the UBA points out that, undeniably, "the problems associated with global consumption can only be reduced if the everyday consumption patterns of people in industrialized countries fundamentally change."

Reese sees it as a joint task and shared responsibility. "We have to bring what we feel as individuals to a collective level." And, he adds as parting shot, make sure you have a reusable coffee cup.

I do, in fact, have one. Just not always in the right place at the right time.