Don’t get married to a market!
That's why it probably feels good to focus on just one market in the beginning. "I just trade the EUR/USD" or "I only trade the ES" or "I'm a Gold trader" are common statements out there. And that's not a bad thing. It's almost impossible to start otherwise, you have to over simplify things in the beginning. Otherwise, you'd never get started trading at all.
But at some point, you should move on and expand your trading world. There are times when it's almost impossible to make a profit in the EUR/USD or when it's better to stay away from the ES. During these times maybe Gold or Crude Oil or AUD/USD are providing really good trading opportunities.
Especially as a day trader, you got to go where the action is. I've seen many traders going under because they kept on trying to milk a dead cow. That's why recognizing when it's time to look elsewhere is one of the most important skills to survive in the long term.
Don't get married to a single market, don't keep on throwing good money after bad just to prove to your ego that you can get the money back from that market. Be flexible, go where the easy buck is.
There's almost always a low hanging fruit…and usually, you know where it is. You're just too stubborn to take it.