Mercedes' Ground Effects

McLaren said they were so worried about Mercedes, have they not been watching this year? Help me explain why the Mercedes can look so good at times and so poor at other times. I don't understand enough about Formula One that you put hard tires and fuel inside that Mercedes. And then you get Louis Hamilton on the radio like Scotty saying, you know, on the Star Trek, I'm giving it all she's got. But let's get on to Mercedes next.