Why are some goals so hard to keep?  Like our goals to exercise more, lose weight or quit smoking. And why do we keep setting the same goals – again and again – even after we fail?

According to psychologist Dr. Janet Polivy, it may boil down to the fact that we’re too optimistic! In fact, several new studies show that the human brain is “hard-wired” to be optimistic – because optimism is what drives us to challenge ourselves, compete, and believe that we can achieve new things. And while that sounds like a good thing, Dr. Polivy says there are times when our optimism can get the best of us, and sabotage our chances of success.

She says it’s because when we’re too optimistic, we tend to set unrealistically high expectations for ourselves. And over time, if we keep failing to meet our lofty goals, it kills our motivation, and makes us less likely to succeed.

Consider a study Dr. Polivy did with a group of chronic dieters. She put everyone on a moderate diet that helped them lose a pound a week, on average. But then, as soon as the study ended, none of the participants stuck with the diet. Why?  Because everyone had unrealistic expectations that they’d lose much more than “just a pound” a week.  So, they figured the diet wasn’t working – and they gave up!

She says this helps explain why 90 million of us set resolutions each year to lose weight – or to quit smoking – but only 1-in-10 of us succeed.  Dr. Polivy says the key to reaching our goals is to be realistic because many studies show that people who make realistic changes in their life generally do succeed.

Sometimes being optimistic can backfire because it can drive us to set wildly unrealistic goals. Like, instead of just vowing to lose weight, we may tell ourselves we can lose 20 pounds in a month! Then, when we fall short of our goals, we give up, and go back to our bad habits.

So, how can we set more realistic goals? Here are some tricks recommended by NYU psychologist, Dr. Peter Gollwitzer:

First: Don’t be afraid to fail. Because each time we fail to reach a goal, it’s a chance to learn from our mistakes, and come up with a better plan to try. And the more we try, the more likely we are to succeed.

Next: Avoid goals with the word “don’t” in them. Like telling yourself “don’t eat junk food anymore.” Dr. Gollwitzer says people are much more likely to stick with goals if they involve DOING something – like saying, “I will eat more fruits and vegetables”.

Another way to set realistic goals: Have an “if/then plan”.  That’s a specific plan to replace a bad habit. So, if your bad habit is downing a pint of Haagen-Dasz when you have a bad day, Dr. Gollwitzer recommends this “if/then” plan:

“If I have a bad day, then I’m going to call my best friend or spend an hour walking my dog.” He says the easier your “if/then plan” is, the more likely you’ll be to stick with it.

The takeaway is this: When you set smaller, realistic goals, studies show your odds of achieving them will skyrocket!