As someone who's been there done that: throttling yourself a little bit is a lot more productive in the long-term.

I used to work to the point of exhaustion. Now I work to a clock I've come up with empirically. This means that instead of having bursts of super productivity followed by weeks/months of tiredness or simple "Meh, that's not interesting" I can trod along, putting one foot in front of the next, with a consistent pace. Day in, day out. You might outsprint me today, but I will be there when you're tired, and I will be walking at the same pace I am now.

I am an orc. I do not stop. I do not tire. I just go. Forever. At a constant pace. I will outplod you.

Persistence is humanity greatest natural asset next to intelligence. Use it. We are very bad sprinters.