And it's worth pointing out a couple of other things most people don't realize:

Almost all of the people you see pictures off with really huge muscles today are/were heavy steroid users. Arnie looks "normal" compared to modern bodybuilders, and he used lots of steroids and put in massive amount of effort (another thing a lot of non-lifters don't understand is that steroid users don't get it easy, what they get is much faster and better recovery, letting them work harder and keep improving beyond a point where non-steroid users plateau) year after year after year. He first won a competition in 1965 after many years of exercise, and got his last Mr Olympia's in 1975 and 1980. The entire competitive field moved massively in that period with

Even more so, you usually see pictures of them that are nothing at all like what they normally look like. When training for Conan, Arnold decided to take one last shot at Mr. Olympia, and went on to win the 1980. Here's what he looked like:
http://www.ironmanmagazine.com/blog/johnhansen/2011/12/27/th...

But he looked like this, minutes to hours at a time at most, while covered in oil and dark colouring to bring out his definition. This is Arnold near or at his peak, after months of gruelling competition preparation, followed by making sure he is hydrated just right and his muscles are pumped for competition.

Outside of competition or exercise situations most lifters will be much less lean (especially power lifters) and will ironically often look smaller as a result of less definition and for many a less V-shaped torso that masks some of the development. I even find myself impressed by guys at the gym that I know for a fact are less muscular than me when they happen to be leaner so their build is more noticeable.

I just did heavy (for me) bench sets this morning. When I do, my chest and arms swell enough that my normally well fitting t-shifts stretch noticeably. I have to keep adjusting my polo shirts. This lasts for a couple of hours, and the swelling wears off.

I'm roughly Arnie's height, and weigh as much as he did at his peak. My body volume is bigger than he was at his peak, but I look much smaller because I have about 15kg more fat than him and 15kg or so less muscle... (I can claim my volume is bigger because muscle is more dense than fat - his overall volume would have been smaller, but concentrated in more muscle on his arms, chest and legs rather than as more evenly spread fat; I believe his waist was 34" when he was competing; I'm 36" to 38").

This is after 8 years of "recreational" lifting, starting at 30. I'm consistently in the gym 3-5 times every week outside of perhaps 2-3 weeks a year. If I started younger, and lifted more seriously, I might have gotten closer in size, but without steroids and far more work I'd have no chance of getting close to that kind of muscle volume and development. I'm not even at competitive levels for regional competitions in either power lifting or body building.

Yet I look more muscular than most guys who worry about getting bulky ever will, but I look tiny compared to well developed body builders much smaller than Arnold, despite a similar body volume.

Another thing most people that worry about this don't realize is that they eat way too little to ever get to even my size no matter how much they exercise. Currently I'm gaining strength at a good rate without increasing my weight thanks to mostly following intermittent fasting with a very high protein diet. Most days I eat 180g-230g of protein... Most people will find they'll be so stuffed they can hardly push more food down if they try that, pretty much irrespective of total calorie intake - getting most of it via lean chicken to give me some flexibility for other meals, still means I have nearly a kilo of chicken for lunch... I'm sick of chicken...

And I am not eating enough to get steroid-eating body-builder big, by far - I currently eat at roughly maintenance levels but varying up and down to get me in a slight deficit on non-exercise days and slightly above on exercise days.