This concept references an interesting phenomenon which occurs in buckets of crabs. If one crab attempts to escape from a bucket of live crabs, the other crabs will pull it back down, rather than allowing it to get free. Sometimes, the crabs seem almost malicious, waiting until the crab has almost escaped before yanking it back into the pot. All of the crabs are undoubtedly aware of the fact that their fate is probably not going to be very pleasurable, so people are led to wonder why they pull each other back into the bucket, instead of congratulating the clever escape artist.
This term is broadly associated with short-sighted, non-constructive thinking rather than a unified, long-term, constructive mentality. It is also often used colloquially in reference to individuals or communities attempting to "escape" a so-called "underprivileged life", but kept from doing so by those others of the same community or nation attempting to ride upon their coat-tails or who simply resent their success.