Probably one of the least enjoyable parts of management is dealing with an employee or direct report who is just not meeting expectations. What makes these difficult discussions so hard is that we often put them off simply because they are so unpleasant. As a result, when we do finally sit down with the person, the discussion either turns into an adversarial rather than a constructive conversation; one or both of us either blows up, talks past each other, or seeks to win the argument rather than solve the problem.
The scenario in our head usually plays out something like this:
"I've seen Sally come in late to work 5 times in the last 2 weeks. I wonder what that's about." At the same time, I don't want to be a micromanager or govern my employees by the clock; I always tell them that I appreciate if they want to work late to complete a task or meet a deadline and to balance that off, I'll give them the benefit of the doubt if they come in late on occasion. "But 5 times in 2 weeks! What is she up to?"
And so rather than raise your observations with Sally, we usually set out to create a story to explain Sally's behaviour. Is her marriage falling apart? Maybe she's having an affair? Why isn't she getting enough sleep? Is she just bored, or worse, lazy? Maybe I need to give her more work?
We then seek out anecdotes and circumstantial evidence to support any of these stories and we begin to interact with Sally based on the emotional baggage that our constructed story has given us. Things go from bad to worse. Whatever might be Sally's issues, our relationship with her is starting to hit the rocks which makes any necessary conversation even more difficult.
The time to have the discussion is after we first notice the behaviour and before we start to construct our own story to explain the behaviour. That is the sweet spot where we can have a conversation based only on facts, "Sally, can I have a word with you? Over the past two weeks I noticed you coming late to work at least 5 times. Is anything wrong?"
Unless Sally has a background as a KGB agent and is now president of Russia, she likely won't deny that fact. Instead she will either try to excuse it ("Yeah, sorry, it won't happen again."), or explain it ("Yeah, sorry, my babysitter is away and I've had to take the kids to my mother's place across town before work. I guess I didn't factor in how bad the traffic is at this time of the morning.")
In either case, Sally is now aware of your concerns. In the case of the excuse, she should understand that you will continue to monitor her behaviour and if it continues, you will have a further fact to share with her, "Sally, when we talked last week, you promised me that it wouldn't happen again, but you were late again twice this week."
In the second case, Sally has invited you in to help construct a common story--one that you can both live with. Perhaps you can help write it with her. "I'm sorry, I didn't know. If it would help, why don't you start 30 minutes late until your babysitter gets back and then make up the time by taking a shorter lunch or working 30 minutes longer at the end of the day?"
Either way, you will have worked to resolve the issue, make sure everyone's needs were met and that productivity did not suffer more than it needed to and avoided all the drama that often goes with these sorts of difficult discussions.