Comment by Tronic2

Syntax of pointers. Easy to use high level languages make extensive use of pointers (i.e. all their variables are actually pointers) but beginners cope with them because no stars or ampersands are required, with the help of GC. Of course they'll get bitten soon and often because it is too easy to create copies of pointers rather than copies of full data structures, and without understanding pointers it's hard to grasp why that happens.