You can indeed unlock any chest regardless of your lockpicking mastery. Despite having no proficiency in lockpicking I was able to unlock a master chest that I found, albeit with great difficulty. As far as I can tell, your proficiency affects the speed at which your lockpick breaks, and perhaps the accuracy of where you have to slide your lockpick.
When you hit on the wrong position, the game makes a distinctive resisting sound and your lockpick shakes. As a result, the easiest way to succeed at lockpicking is to adjust your position a few spaces over to the right or left, make a very brief unlocking motion to see if the lockpick shakes or not, and if it doesn't continue sliding it in. If the lockpick shakes during the middle of twisting it in, don't change your starting position but instead just test going either right or left from the shaking position to see which direction is the correct one.
The correct movement will not change in-between successive failed attempts at picking the lock(but will change if you exit the lockpicking screen or reload your game), so even if your lock breaks, use the information you gathered from your last attempt to try and succeed with your next one.