The title does explain my question quite well, but here is some more details about the option itself. The -novid launch option for Dota2 can be set through the Steam Library page. It disables Valve's intro (The guy with the valve at the back of his head) before starting dota.
Here is a picture of my launch options:
Best Answer
You need to put a space between every launch parameter, otherwise it won't work.
Like this:
The reason is, that the operating system only treats each parameter separately when separated by spaces. Then it puts the count of the parameters into a variable, known in Programming as argc, while the parameters reside in argv. So without a space, Dota 2 (respectively the Source Engine) would only receive 1 parameter at all and not recognize any of them, because they do not match any option.