Foundations
A margin call is a demand from a broker or lender for more collateral, and it is the mechanism by which falling prices force selling regardless of what anyone believes. Understanding margin is understanding why markets overshoot: leverage turns a price decline into a cash demand, and a cash demand into more selling.
How leverage creates the trap
Buying on margin means borrowing to buy more of an asset than your cash allows. The position is collateral for the loan, and the broker requires the collateral’s value to stay above a maintenance level. When prices fall, the buffer shrinks; breach the level and the call comes: add cash today, or the broker sells your position for you, at whatever the market will pay. The same logic binds hedge funds, banks and derivative traders through collateral agreements, just with bigger numbers.
From one call to a cascade
Margin calls synchronise selling. A sharp fall hits every leveraged holder at once; their forced sales push prices lower, which triggers the next round of calls. This deleveraging spiral explains one of the strangest sights in market crises: investors selling their BEST assets. In a true squeeze you sell what you can, not what you want to, because gold, Treasuries and quality stocks are what still have bids. It also explains why “everything falls together” in a crash: the seller’s portfolio, not the assets’ merits, drives the flows.
Reading forced selling in the wild
The tells: violent falls with no fresh news, safe havens falling alongside risk assets, and sharp snap-backs once the flows exhaust themselves. When our coverage says an unwind “fed on itself” or losses became “self-reinforcing”, margin mechanics are usually the engine underneath. The events differ; the plumbing repeats.