Counter picking someone can be detrimental and can often lead to snowballing them so bad that you put them out of the game for good. You see this a lot with champions like Xerath mid who can really wreck a team 1v5 but not if they have to lane vs a good fizz or zed player early game.
However, counterpicking someone just for the sake of champion advantage when you have no experience on the champion is awful and can have quite the opposite effect.
For example, Morgana can be seen as a counter to pyke in some ways. But its a counter with a very clear weakness towards pyke as well. Morganas spell shield has a 20+ second cooldown while pykes q is half that. Experienced pyke players will actually find a morgana lane to be very easy if the morgana is inexperienced.
As a rule of thumb especially in low elo, a counterpick isnt really a counterpick if you never play the champion. Just stick to what you know, even if you are disadvantaged slightly.
