A common theme associated with OKRs are stretch goals. The idea is that if you target a more ambitious outcome than is comfortable, you're more likely to achieve it.
While stretch goals are great at pushing people further, they can also have detrimental effects. You want to make sure that your employees are ready.
First, by definition there must be room for growth for your products or services. If you cannot sell or achieve more just by the hard work of your employees, you'd be setting them up for failure.
It's preferable if your organization's culture isn't too rigid. Missing objectives on a regular basis opens people to perceived failure. In a culture that rewards risk, it's usually not a problem.
You should be adequately staffed. We've seen it: a company struggling and its management thinking moonshots will save it. If your employees are already overutilized, they won't have time to make headway on new things.
Finally, there should be trust in your organization. Trust between peers and trust of the leadership that goals won't be used to draw a bell curve and cut raises.
First, you absolutely need to communicate expectations beforehand. This is actually the only thing you need to do. So say it, repeat it, and lead by example.
It's also useful to introduce stretch goals gradually. Aiming at something difficult but not impossible takes practice. There's no point in being wrong for all your goals.
Tip: make sure you can identify stretch goals in your goal management software (or spreadsheet).