"It worked when I showed it to you"
You built something. It genuinely impressed people. You clicked through it yourself a dozen times, your co-founder clicked through it, you recorded a little screen capture and sent it around and people said yes, this is the thing. Then you shared the link with actual users — strangers, people who don't know what you intended, people on different devices and slower connections and with completely different assumptions about what a button labelled "Submit" is going to do.
And it fell apart.
Maybe it was a broken login. Maybe data disappeared. Maybe it worked fine for the first three people and then something went wrong on the fourth and you have no idea what they did differently because you weren't watching. Maybe it just looked slightly wrong on a phone and people quietly left.
This is one of the most common and most demoralising moments in vibe coding. You did everything right, in the sense that the thing exists and does the thing. But somehow it doesn't work. And nobody warned you that working and working for strangers are two entirely different problems.