It could be a muscle group. It could also be your starting strength, or rate of force development,or ability to maintain total tension,all requiring a different solution. The point is to really analyze where you fail in the lift and then bring that up.An unwavering devotion to where you are weak is the only way to get stronger. Because we are always just as strong as our weakest link.Everyone likes to train their strengths, cause its 'fun'. Training your weakness is what makes you better.
And you have to find out where YOU are strongest.If you dont know where you have the best leverage it will be hard to maximize that position. ANd sometimes that position ain't exactly "pretty". as long as its( relatively) safe( I mean how safe can trying to ever increase the maximal load you can move be?) go with it.Seek out, analyze and attack your weak links, wherever they may be or wherever you find them and keep getting better!