You need have a specific target, otherwise you're just shooting in the dark and you'll get bored easily. But if you say, "I want to make a web site that does A

You need have a specific target, otherwise you're just shooting in the dark and you'll get bored easily. But if you say, "I want to make a web site that does ABC", or "I want to make an app that does XYZ", you won't just be - as mkremer90 said - shooting in the dark at a whole bunch of different technologies