The tighter your control at the onset of a submission hold the better you will be able to retain it against defensive countermeasures. If you have just enough mechanical at the onset to perform the lock, any defensive will take you below the threshold required for completion defensive movement always reduces the mechanical of your submission hold. You need to over budget for the anticipated resistance. If you have twice the amount of mechanical tightness required to the limb at the onset of the hold, and your opponents defensive reduce this by a quarter, you will still be well above the threshold required for success. So right from the start, seek maximum mechanical tightness, so that the inevitable resistance will not be enough to you.