Whats the reason humans can't climb trees as well as apes?

Well i have been climbing trees for some time now and i still can't get anywhere near as good as a chimp. The thin trees are easy to climb but when it comes to the thick ones, its brutally difficult. Watch this video and notice from the beginning to 0:08. I have tried to climb a tree like that many times and every time my feet slip or i just can't get a good grip on it. How do they do it!!!!