I heard a quote from the great John Carmack that resonated with me the other day.
Focused hard work is the real key to success. Keep your eyes on the goal and just keep taking the next step towards completing it. If you aren't sure which way to do something, do it both ways and see which works better.
When building my first SaaS company I had a very binary approach to getting things done. I made big pushes to get things done. I acted like everything was on fire all the time. I would pull all-nighters and work 16 hour days.
I had notions that "if I can just fix/write X then the company will live". Sure I might get more done for a day or two, but by Wednesday I was useless already recovering from Monday and Tuesday and by Friday I was frustrated I wasn't getting anything done and then I felt guilty for not working.
I was either sprinting or completely exhausted.
It was crushing to put in those sorts of hours only to find out that something you built wasn't going to work.
I don't regret the experience, it shaped who I am, but if I could do it differently now, I would take the endurance approach.
Putting in the right effort at the right time, consistently, allows you to enjoy the learning and build strength, resiliency, and momentum over time.
P.S. I can't recommend Masters of Doom enough. It's a phenomenal book by David Kushner telling the story of the John Carmack and John Romero creating Id software and building the first 3d games for PC. I'm especially fond of the audio version which is done by my favorite narrator, Will Wheaton.