In my opinion in order to be successful in trading you must approach trading as a full time. As a trader, you are essentially a small business owner and you must research and strategize to maximize your business's potential.
I don't think that it has to be like that.
You can trade even you're not full time on it. You can be successful with trading despite not fully committing your time on it but it's not your main source if that's what it is.
Traders that source it as their main income has to be good at their most trades.