... because it seems to magically fit in everything and the kitchen sink. lol Maybe not that much but it is damn close. This backpack fits my daily needs very well. Let it be noted that I am not a soldier, hiker, camper, student or anything like that. I am just a regular guy who does alot of walking every single day. It's my preferred method of travel and great exercise. My job is not close to my home and during the course of the day I need access to alot of my stuff. Change of clothes right off the bat since I am not wearing my work uniform around town. Jacket/hoodie if the weather calls for it goes in there. Lunch goes in there and that is not a small little brown bag, I need a big lunch since I have such a long day. My headphones go in there when not in use, glasses and sunglasses and their cases, extra items (keys, pens, pocket knives... anything I can't be carrying around while I am working) and anything I might need to bring somewhere that day. Also I grocery shop for myself on an as needed, by the day basis. I make a list for that day and pick it up on my way home. Those things also fit in this backpack. I am very pleased overall with this pack's amazing capacity. It has several sections to seperate stuff into and adjustable straps of all kinds to just customize the bad to your own fit. I also love the color, I'm a huge fan of the more military looking green of the bag, I'd love it more if it was camo but not complainin. Oh and I read some reviews mentioning the lack of hydration system or whatever and I suppose that could be an issue depending on your own particular situation but it isn't for me because I carry water bottles all the time (which btw ALSO FIT IN THE BACK PACK!!!) and don't need a hydration system because that is what I have free hands for. Highly recommend this guy!!!It is better than the roll around luggage pack I was using. This looks great and goes well with my new military bug outfit. Hope I never have to use it though.The bag is designed well, but uses relatively cheap material may deter people from using it for daily use such as school, but it is why it is affordable. I used some fishing line and a needle and resewed the lower seams to help it handle heavy stress since the reviews had me worried and the material is basically sprayed coating on the inside. If you expect to be in the rain with it for too long I would get a poncho . Hard to adjust it without another person so the weight is not being carried on my shoulders but I did it where as my luggage was painful even for any short distances that I couldn't roll it . It is the main reason I dished out the money for a better bag. Just get the nicely padded straps adjusted so the weight is on your hips and none is on your shoulders. I had to pull the waste one out all the way. I had to take it on and off fifty times but it is very comfortable for not having a back brace or wheels and such...It holds a lot and has lots of pockets zippers and webbing for attachments. I plan on attaching my bed roll and water system to the outside of it. With all the extra space I can bring lots of extra finish line and needs...Hope the zippers and buckles hold up.To be truthful, I did not expect much of this purchase. With high end bags running into he several hundred dollar range, I thought, for what I was using this for, it would be sufficient. I can assure you this is much more than "sufficient". To the point, and, in an effort to calm the pack purists, I am not using this for combat deployment, rappelling, or any attempted emulation of a Bear Grylls episode. That said, for what it is, I doubt I will ever wear this thing out. It has a bit of heft to it, and,most everything you would want in a low priced pack. The straps are comfortable, the loops are plentiful, and, the MOLLE loops are firm, yet pliable. Attaching my BK to it was effortless, (you should hope it would be) and it held quite firmly. There are more pockets than you can imagine, and misc loops are provided for small carabiners and the like. Shoulder straps are equipped with lateral chest straps to keep the mains from sliding, and, there is an adjustable waist loop that easily adjusted to a size 38. ( Someday I would like to see if it will adjust to a size 36;) Zippers, as expected on anything new, are a touch stubborn, however, quite usable. I would not say it is waterproof, more water resistant, with a flap over the vulnerable zipper area to shed the water. I am not sure on fabric saturation. Lateral handles allow for 3-way transport, and they are well made in their own right. All in all, for the price, I do not see how you can go wrong with this. TONS of room at a reasonable price, great purchase.I bought this pack to carry supplies for our hiking in Arizona. Specifically, I wanted a pack that had lots of pockets and straps to organize the things we carry such as a couple sandwiches, some fruit, plenty of water, some first aid supplies, cell phones, camera, etc. This one seemed to fit the bill.The main zippered pockets are pretty good - they have two zippers so you have some flexibility. There is also a divider in the main pouch that helps organize the larger things. this is a bit fussy, but I'd love to have two zippers on those little side pouches. those are the locations where I store phones, wallets, keys, etc, Since they zip all around the pouch from bottom to bottom, it's easy to leave a gap in the pouch (at the bottom) through which valuable items can fall out. I'd prefer two zippers, or one zipper that goes from middle to middle across the top.The zippers are large-toothed and seem rugged, though they are plastic and not the smoothest to close. The pack fabric is heavy duty and should be very durable. I found the pack to be comfortable even with a load. This was a ten pound load, mind you.....I'd buy it again - it seemed to be a clear choice as I compared packs on Amazon.