I will go ahead and claim, that even seemingly trivial programming tasks are astonishingly difficult.

http://www.cs.princeton.edu/introcs/42sort/

According to Knuth, the first binary search algorithm was published in 1946, but the first published binary search without bugs did not appear until 1962.

http://googleresearch.blogspot.com/2006/06/extra-extra-read-...

http://www.cs.princeton.edu/introcs/papers/bentley-binarysea...