There's a leadership philosophy which emphasizes not revealing your fears. "Never let on that you have fears. If your team sees that the leader is worried, it will make them discouraged and even more scared themselves."
I used to believe in this, when I was just starting out at Microsoft. My first manager subscribed to this theory and would tell me, "No matter how you worry on the inside, never let it show to your team." He lived this philosophy, and never told me about any worries, even as that specific project started faltering.
Many years later, my management coach at Google countered this theory. "The most effective leader is one who is straightforward, and comfortable in their own skin," said Brian, the management coach. "Think about Bill Clinton. Effective leaders let you know when they're nervous. They do it in a calm way."
I've subscribed to Brian's approach for 6 or 7 years now, and I find it effective. If the team knows that the leader is nervous about X, they'll focus on that rather than being distracted by Y. Seeing the leader's vulnerability makes the team feel a stronger connection. It's also a relief for the leader to be honest rather than trying to bottle up all of the worries.
There are a few keys:
1. Spend most of the time describing potential solutions, not dwelling on the problem.
e.g. "I want to reduce the likelihood of Bob getting defensive at tomorrow's meeting. I sent out an agenda beforehand so he can be mentally prepared. I invited Joe who is a calming presence. I also will limit the time we spend on controversial topics. But I'm still worried that all of these are not enough."
Don't spend all your time catastrophizing: "I'm worried that Bob will get defensive at tomorrow's meeting. If he does, it might set the tone and influence Phyllis and Janet. If all three are opposed to the contract I proposed, it could kill the deal. If we don't get this deal, we'll fall short of our revenue targets."
2. State the situation in a calm tone of voice.
3. Make it clear that you welcome help, but that you are not relying on the help, and that you will be resourceful in the situation regardless.
Say "This is my plan, but I'm not 100% confident it will succeed, and I welcome suggestions." rather than "What are we going to do?! This is horrible!"
I met a startup CEO a few years ago. The startup started going through tumultuous times, and the CEO never revealed any worry. He broadcasted an aura of great confidence. However, everyone else in the company was already highly worried because they could log into Google Analytics and see that there were major issues with traffic levels, user acquisition, and revenue. The CEO acting stoic just made people feel out of touch with him, and less able to brainstorm together.
There's always a roller coaster in every startup, no matter how successful it is. It's better to come across as a courageous human than a stoic robot.