Because college will help you judge how reliable something on Wikipedia is and help you go beyond just knowing facts and how to interpret them and form opinions about them.

Hum... I didn't need to attend college to realise I lacked knowledge. I went there because I wanted more knowledge and tools to serve me in my life.
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You did it backward. The things you say you realised, I wonder how come you didn't realise them before attending college. Based on what you said about "the  experts out there that have a depth of knowledge in a particular area", how come you didn't make this realisation with your first contact with a teacher?  In any case, nope, it didn't make me feel more or less intelligent. It did make me realise that I was capable of some things for which I doubted myself.

Essentially it was re-learning so many aspects of life. In particular the complexities and greyness of life, history and issues. I was very humbled and think I cam out the other side far better for the experience.

Many people are chiming in about direct financial benefit of doing it. I tend to agree, and one of my great accomplishments was graduating with zero debt thanks to scholarships and work. I would say while my degree has not translated to my field of work, the skills I learned along the way tangentially made me more able to handle the various responsibilities and decisions I face daily.

I would advise people if possible to do so, but not if you think University is this golden ticket to middle class safety. Avoid as much debt as possible, have a year off before going or take a break while attending. I have witnessed far too many 20 somethings spending 400-800 a month paying off loans and having to move back home and take first job they can get. Enjoy the time, evaluate your options and what has value to you. I think an 18-24 year old taking their time with major life decisions is understandable.

I'm in college now, and I completely agree with what you said. Honestly, I felt more intelligent and motivated in high school than I do here. I'm a Mathematics major and so far it's been challenging, but not as bad as I thought. I expect it to get much worse next semester when I start taking Calc 3 and the more pure math classes. Seeing some of the students in class make you feel really inadequate (that may just be me) and you always feel someone else is just better than you in every way; that's the humbling part. Sorry if there is errors here I'm typing on my phone.

I won't argue against that. But prior to college you're given straight A's due to grade inflation (well, still the case in college...) and you're told that you're part of a special minority for getting into college.

But what I realized was that even though I was in a small minority, that amount of knowledge you gain in college is really, really small. I also learned that the world's a bigger place. Congratulations for you if already knew that going into college.

Both ... it was never constant (both undergrad and grad). I have no regrets though. It molded me into a conscious consumer and I'm much more analytical in all my activities.

Being a part of a minority because you go to college doesn't mean that you're more intelligent than the majority who doesn't go. It means you'll get tools and means to use this intelligence in a certain way that most who don't attend college won't get or develop.

That's may be true, but I'd argue that money is overrated, if not unnecessary and there are many fields where you need to go to college to have any chance of being successful.

Also, on the direct question. I think the biggest shock is if you attend somewhere you feel very average with all the professors. Then there is a sort of intelligence or awareness culture shock when you have conversations with general people. Going from a place where having a good knowledge of current events and politics was expected to one where people tend to be more concerned with gossip about some celebrity is jarring.

I agree with this.