If you are right into handline fishing -which is a very pleasurable search, incidentally-- possibilities are you've experienced tangled lines. It takes place quickly: you lay the line on the ground, boat or pier area, and when the lengths of line are disturbed, fibers relocate into, under or over other hairs, which, when pulled tight, could trap those disturbed lines. This results in snarled lines of loose knots and loopholes.
You could decipher the tangle by pulling out the end. If the tangle looks also tough to unwind, you could cut off completion, pull on it to see where it results in in the tangle, after that pull on that portion until completion slides out. Do this time and again and also pretty quickly you would have unraveled the tangle. Retie your incurable knot.