4. You’re slacking off.
While this isn’t all to common among guys looking to build size, doing too little can hamper your growth. Your muscles respond to stimuli - growing back stronger and more resilient. If the stimulus presented isn’t enough to cause a major change or disturbance in your body, you aren’t going to see much (if any) results. Ensure that you’re training consistently at least three days a week to produce desired changes in your physique.