Poor guy! Look at his little, chicken arms! Any veteran lifter knows exactly how he feels. There are times when a 20lb dumbbell feels like 40lbs. That’s when you have to dig deep and ask your body to perform even when it’s rebelling. The trick is to get it to do SOMETHING in a positive direction. You certainly can’t just pack up and leave the gym because that sets a bad precedent psychologically.
If 20lbs feels like 40lbs, my suggestion is to grab the 12lb or 10lb dumbbells and proceed with your workout. Don’t despair, don’t quit…just adjust and keep right on going!