my employee keeps flipping from great to terrible

This post was written by Alison Green and published on Ask a Manager .
A reader writes:
I have a direct report who was at one time my star performer and was on track for leadership. She had some challenges in her personal life over a couple years, and over time her performance slipped until it became a problem. Accuracy errors, chronic lateness, and a general negative attitude that brings her peers down have come and gone over the last two years. It will get really bad, we’ll have a serious conversation about whether she wants to be here, she’ll pull it together for a while, and then she’ll backslide.
I’ve continued to hold her accountable to her job duties, but my question is whether I have to continue to invest in being excited, motivated, and supportive of her getting herself together over and over. It’s exhausting and disappointing to keep thinking she’s going to finally get back to where she was and then have her go down the same path over and over. Do I have to act like I have full faith that this will be the time she maintains performance, or can I be honest and tell her that when she maintains it for six months, we can start talking as though it’s the new status quo? She just emailed me her aspirations to be in leadership and the ways she’s going to turn things around, and all I can think is, “I’ll believe it when I see it.” But I also don’t want to demotivate her by giving the impression that I don’t think she’ll actually do what she says she’s going to.
I answer this question — and three others — over at Inc. today, where I’m revisiting letters that have been buried in the archives here from years ago (and sometimes updating/expanding my answers to them). You can read it here .
Other questions I’m answering there today include:

I don’t want to eat all my meals with a colleague when we travel together
Exercise ball chairs in the office
Information interview requests from fellow alumni

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