Public flow data tells you what happened, never who

Some markets publish end-of-day summaries showing which brokers accounted for the largest share of a name's volume. Wherever that data exists, an entire cottage industry grows around inferring intent from it. We have partial equivalents. And the same caution applies, only more so. What flow data genuinely tells you: unusual concentration happened. One participant or venue accounted for far more than typical, which is a real fact and occasionally a useful one. What it does not tell you: who, or why. A single large print can be a fund building a position, a fund exiting one, a hedge against something you can't see, or a facilitation trade that has no directional view at all. Every one of those looks identical in the summary. So it's usable as a flag. Something happened here worth looking at — and unusable as a signal. The failure mode is treating concentration as direction, and it's a comfortable mistake to make because the story writes itself. Use it to decide where to look, never what to do.