Why do memory cards fail, and can data be recovered?

Because flash memory wears out, controllers fail and cards are physically abused — and recovery is frequently possible, provided you stop using the card immediately, which is the single most important thing and what people reliably get wrong.

Why they fail:

Wear. Flash cells tolerate a finite number of write-erase cycles. Cheap cards with limited wear levelling fail far sooner than their capacity suggests.

Controller failure, which renders the card unreadable even though the memory is intact — the most common sudden death.

Removal during writing, which corrupts the file system and is entirely avoidable.

Counterfeits, which are widespread: cards reporting far more capacity than they contain, writing data that silently overwrites earlier data once the real capacity is exceeded. The failure appears only when you try to read old files, which is usually after an event you cannot repeat. Testing a new card's true capacity with a verification tool is worth doing.

Physical damage, heat, moisture and static.

Age, since unpowered flash loses charge slowly over years — which makes cards a poor archive medium.

What to do when a card fails:

Stop writing to it. Do not reformat, do not shoot more, do not let software "repair" it. Every write reduces what can be recovered.

Make a sector-level image of the card and work on the copy, not the original.

Try recovery software on the image. Deleted and lost files frequently remain intact because deletion usually only removes the index entry — photo and video recovery succeeds far more often than people expect.

Physical or controller failure requires a specialist, which is expensive and sometimes the only route.

How to avoid the situation: buy from a reputable seller, since counterfeits dominate marketplace listings; format in the device rather than on a computer; use several smaller cards rather than one large one; offload and verify before erasing; replace cards periodically rather than until failure; and never use a card as storage — it is a transfer medium.