Most harmful misconception of beginners about programming? [closed]

Question

Re-inventing standard library functions/classes.

After going through a language book/tutorial, most beginners - knowing how to handle strings and numbers - will invent their own date functions, their own 'compression algorithms', their own SORT implementations.

Oh, and they always spend their first day searching for clrscr();.

That because their program compiles and runs it does what they expect it to do.

That if their code doesn't compile or work, it is because of a bug in the compiler.

Maybe not the most harmful, but they usually can't estimate how long stuff will take to be done, they think it can be done much faster than it really must(including me).

As for harmful stuff, good companies usually keep beginners away from where they can do much harm. They are usually encouraged to work by someone more experienced, so they can learn better.

That if their program works on their own computer, then it will work on everybody else's computer too.

"But it works on my machine!"