I learned that putting more pressure on myself wasn't working, that there isn't a linear relationship between pressure and results. Instead, there is what I call a sweet spot, beyond which more pressure decreases results instead of increasing them.
I'm definitely most effective when I'm happy. If I overwork myself, I quickly get into a negative feedback loop of "never being caught up and satisfied with work."
I learned to internalize the idea of keeping myself happy (stable work/life) first, as in the long run this is the most effective situation.