I admit that I’m prone to an optimistic outlook, a belief that most problems can be tackled with hard work and the right mindset. I’ve read the research that indicates that positive thinkers tend to do better in school, work and life. Perhaps I even assumed that optimism was infectious and that people wanted to work with a confident, hopeful leader. In the true spirit of optimism, how could this possibly go wrong?

Then I found out from a colleague that he didn’t find my optimism nearly as reassuring as I did. We were in the middle of a high-stakes research project with a small window of opportunity to write an article for a prominent academic publication. To pull this off, we needed to complete a complex analysis, do a round of additional research, and actually write the article, all while working on several other projects and operating on a thin budget.

To me, this seemed like a feasible, interesting challenge, and I enthusiastically dove in. Then at one critical meeting, a more junior colleague turned to me and said, “Liz, I need you to stop saying that!”

“Saying what?” I asked.

“Saying that thing you always say — ‘How hard can it be?'” I looked puzzled. He explained, “You say that all the time. ‘How hard can it be? We can do this. After all, how hard can it be?'”

I recognized what he was saying and began to explain my logic: While I was working for Oracle Corporation, a small but rapidly growing company, I had been thrown into management at the tender age of 24 and was told that I was now in charge of training for the entire company and was tasked with building Oracle University and making it work in globally. I learned to say to myself, “We can do this. After all, how hard can it really be?” Now, I explained how this growth mindset had worked beautifully for me and many of my colleagues over the years. Yet steadfast, my colleague reiterated, “Yes, but that is what I need you to stop saying.”

“But why?” I probed.

He paused and said, “Because what we are doing is actually really hard, and I need you to acknowledge that.”

He wasn’t opposed to the idea that our enormous task was doable; he simply wanted me to acknowledge the reality of the challenge and recognize his struggle. He didn’t want me glossing over the challenge with my coat of optimism. So I did admit, “Yes, what we are doing is hard. It is really, really difficult.” I then assured him that I would do my best to stop saying that thing. Meanwhile, in the back of my mind I told myself “Sure, I can stop saying that. After all, how hard can it be?”

Is it possible that a can-do attitude that worked so well for you as an individual contributor may actually work against you as a leader? When you play the role of the optimist, you may undervalue the struggle the team is experiencing or their hard-fought learning and work (or give the impression that you do). Your staff may wonder if you have lost your tether to reality. And, when a leader seldom focuses on the problems, it leaves more junior managers to worry about those risks. In fact, by being too optimistic, you may actually be putting your employees in the role of having to play the “sensible pessimist.” Or worse, you might be sending a message that mistakes and failure are not an option because, after all, “How hard can it be?” And yet wise managers know that mistakes are inevitable, and that failure is just the price of creativity.

Having coached many executives, I know that senior leadership ranks are filled with glass-half-full types (in fact, one might need to be an optimist to cope with the inherent pressure of these positions). Consider how Nike, Inc.’s chief of global design, John Hoke, sparked a transformation in his organization once he realized the restrictive impact his and his management team’s optimism was generating. John gathered his senior leaders for a week-long offsite to explore new thinking in design and how leaders can multiply the talent inside their organization, which I helped facilitate. As I described the profile of the optimistic, creative, energetic leader, John and his team quickly recognized their own reflection and were curious how they might be inadvertently diminishing capability and ingenuity in others. John asked that we pause our agenda to better understand how his own hopeful style of leadership might actually be causing some angst. His team explained the extraordinary pressure they felt to deliver flawless design, every time. With the London Olympics around the corner and a brand promise to sustain, the group insisted that there simply was no room to fail.

With John’s encouragement, we decided to define a space for experimentation. We rapidly laid out their various work scenarios into two buckets: One where failure was OK and the other where success had to be assured. The group debated each until they agreed on every scenario. Within an hour, they had created a playground — a safe space for their teams to struggle and potentially fail without harming their stakeholders or their business. This thinking rippled across Nike’s design community and sparked leaders like Angela Snow, VP of creative operations and Casey Lehner, senior director of global design operations, to introduce the “risk and iterate” performance goal that encouraged each team member to identify something they would take a risk with and then iterate solutions throughout the year. This effort legitimized the possibility of failure and created safety for designers to tackle the scary problems.

John Hoke and his management team didn’t lower their aspirations or become less optimistic about the capabilities of their team. But, by acknowledging the downside and recognizing the messy, iterative path of innovation, they liberated their team to go bigger and reach further.

Go ahead and be optimistic. But first, be sure to acknowledge the downside so your team is free to explore the upside.