This will always be difficult, no matter how many times you do it. Here are a few ways you can approach the situation.
First, identify your objectives in advance. Knowing what you want to accomplish in the conversation will help you be as clear as possible. You should also allow for a balance of power.
When you’re bringing up a tough issue, first allow the other person to explain the rationale for their behaviour. Giving your employee some power will help them to not feel threatened.
It’s also important to be specific. Avoid general observations that might seem vague or come across as a personal attack. When bringing up a sensitive topic, you can also acknowledge that your perspective is subjective. If you frame problem behaviour as an observation, it leaves less room for argument.
Just be careful that you only offer room for negotiation if you are actually willing to consider the other person’s input. If the topic is not negotiable, be firm and direct without leaving room for debate.
Fairness gets results
You should also put the situation in context, as this will essentially hold the employee accountable without attributing blame. This will in turn let you treat the situation as a learning opportunity, which could actually lead to growth.
Finally, validate their feelings. Even if your point of view is non-negotiable, you want to acknowledge how the other person might feel. You want the other person to leave the conversation with dignity, and their self-esteem in tact.