By staying natural, you:
Will never have an impressive physique. You will always be shredded-DYL or Big-Fat. Unless you have a ridiculously good frame, you will never look like you lift in a shirt.
Your test levels will be much lower than test users, therefore, putting you on a disadvantage in the dating scene, especially if you're in your 20's. You will never be sexier and fuck better than a juicer.
Your general well-being will be much lower than juicers. Higher test = better mood = more productive = happier life.
Even if you make impressive natty gains, you will lose most of them by the time you reach 30 as your test levels will start dropping