Amazing how fragile my discipline is at times.
My discipline improved a lot (almost 100% regarding not taking trades I shouldn't take / about 50% regarding taking trades I should take) when I made this my number 1 rule: When you are sleepy, bored, frustrated, ecstatic, depressed or scared, do not open any new positions.
In hindsight, of course, I look at the charts on periods I didn't trade and I see all the opportunities I missed, I should be rich by now, etc... but... It's so much easier to be profitable for the week, month, year when you have zero fuck-ups.
Obviously, it also improved my risk-adjusted returns.