What almost slipped through the cracks last week?

Last month I almost sent the wrong invoice to the wrong client because I was juggling three different threads in my head and none of them were written down anywhere. I caught it ten minutes before it went out, but it made me sit with how much of my business actually lives in memory instead of in any real system.

I am curious how common this is. Has something almost slipped through for you recently, a follow up, a payment, a promise to a client you forgot you made? What was it, and how did you catch it, or did you not catch it in time?