Contrary to popular belief, failure is not when you can't force out another rep without a spot. It's when you can't complete another rep without breaking your form. The key to get the most out of your training is right here - the last rep should be all you can do with good form. Squeezing out a few extra reps after your form has deteriorated will put more pressure on the secondary stabilizing muscles instead of working the targeted ones.

Besides, you set yourself up for injury by taking more than the body can handle. You know you've lost your form on a bench press, for example, if you arch your back on the lift, or start swinging the arms and rocking the body on a biceps curl. Also remember to start each exercise with good form by taking light weights. Trying to impress your buddies with the amount of weight you can lift is like trying to impress the ladies with how many beers you can gulp. So, focus on the technique and muscle your're working and don't worry about completing a set number of reps with a certain weight. Who set these standards anyway?