Yisela said: "I have heard lots of professionals saying some people just 'don't have it', aesthetically-wise. I don't agree." This is certainly a viewpoint that is either right or wrong, and the conclusions that you'd draw from that are very different. If a tone-deaf person can learn to sing, then tell him to try as hard as he can. If he can't, then he's wasting his time, right?
Before I started taking art classes in high school, I was a big math and science guy. I was good at calculus.
You know what doesn't happen in the math field? People skipping algebra and trigonometry, jumping straight into calculus, struggling, and then throwing up their hands and saying "I just can't do math."
Sure, some people are better at math than others. Some people flee from math because they hate it, and some people just aren't able to grasp higher concepts (one of the smarter people I know got tripped up on his college differential equations class!). But there's a logical progression. Learn counting. Then addition. Then subtraction, multiplication, then division. Then math with negatives. Then equations and exponents. Then polynomials. Then integrals. And on from there. Note that this process takes place over a child's entire education.
Point being, while there are some true math prodigies, most people learn it progressively and systematically. And yet, people go into the art world and expect people to just "have it". It's not like that at all, though! There's a reason we spend a lot of time teaching kids how to write - dexterity takes practice. There's a reason why art classes often focus on still-lifes - it teaches you how to see something and translate it to your media. There's a reason why plenty of designers start out designing boring forms for their company - it teaches mastery of the software tools and more minor design execution skills which will help you design new things more quickly later. There's a reason why we do critiques - it teaches designers how to think and imparts wisdom from people who have been doing it more.
Worth noting too that for every prodigy in any field, there are probably 100-1000 people who are in the trenches of the same industry, doing great work but not posting it on the Internet. The beauty and curse of the Web is that it shows you the best of everything. I look at other graphic and web designers out there and feel like an utter failure, and yet somehow I've been blessed to have jobs where I fit in and do good work.
So, with all that in mind...
Improving upon knowledge
Read. Do. Revise. Revamp. Repeat. If you like logos, read Brand New or design firms' blogs to learn more about the industry. Find a project you care about and do a logo for it. Ask design friends (or us!) for a critique. Make it better. As long as you're getting better, you're continuing to set yourself apart from the people who don't. And believe me, not everyone in your design school is getting better.
Picking yourself up post-critique
I like to think that for every person who gets shredded in a critique, there has to be a person who was unwilling to ask. Which person gets better in the long run? I noticed that you did a critique on this site. So did I! My critique got some positive responses, some really negative ones, and some really thoughtful ones in between. Some advice I'll accept, some I'll reject, but my menu today (as well as the future rollout of it) is better than it was before because I was willing to put myself out there and hear criticism.
Another way to look at it: Everyone is a critic. When you design something and put it out there, your work will still be critiqued, except it'll be done by people who can't speak the design language as well, won't be able to make it better, who don't know or care about you. I'd rather hear it from a small group of designers pre-launch than a large group of everyone post-launch.
There is a proverb: "Do not reprove a scoffer, or he will hate you, Reprove a wise man and he will love you." I don't know if the wise man loves being reproved, but he loves the person who does it because he knows that he can become wiser still. Be willing to accept hard truths and use that feedback to make yourself better. I think that advice would apply to any field, and if that sounds like something you don't want to do for the sake of design, then and only then would I say that you might not cut out for that line of work.