If you're learning a new exercise or trying a PR on weight, you can try a few things to break past your "sticking point." 1.) You can use lighter weight (or an easier exercise) and hold that sticking point for time. 2.) You can use a HIGHER weight than what you can lift. Push or pull on this as hard as you safely can. 3.) You can use a lighter weight (like method one) and just do partial reps through your trouble spot. This probably shouldn't be the bulk of your training, but can help you bust through certain plateaus!