The sly fox is a shrewd crook. He never produces anything himself, he'd rather just take from others through trickery. He doesn't even have a home. He finds himself a cave where rodents and insects live and chases them out and makes himself comfortable. However his trickery catches up with him and he eventually falls into his own trap. To catch the fox the hunter sets up a fake cave equipped with a trap. When the fox devilishly makes his way into the cave he is finally caught and his life of injustice is over. (HaKol Yishabchucha - Birchas HaShir)
This is the meaning of the pasuk in Yirmiya (17:11), says the B'Soraso Yehgeh. "Korei Dagar V'Lo Yalad, Oseh Osher B'Lo Mishpat, BaChatzi Yamav Ya'azvenu", the Dagar bird whistles and all the chicks follows him thinking the Dagar is their mother. However when they get older they will realize the truth and leave the Dagar empty.
Some people prefer not to build anything on their own. They prefer to sit idly while others build. Then they set their eyes on fruits of other peoples' labor and scheme to take it from them through cunning and guile. Any scheme based on trickery will eventually collapse. Then all that you have amassed from others will disappear, leaving you caught like a fox in a fake safe haven.
The fox sings (Yirmiya 2:13), "Hoi Boneh Baiso B'Lo Tzedek", woe is to the one who builds his fortune bereft of any sense of justice. This unjust wealth will eventually become his downfall.