You might look at it another way - how many trades should a trader have OPEN simultaneously? I'm no genius but in my experience, it's possible to review 20 charts and in the next 5 minutes find an entry point on every one, long or short, over greater or shorter time frames. But then you have to find their exit levels, keep these under review, and manage the position and risk etc. etc. on all 20 - great territory for running into a ****-up.