Most conventional wisdom is to go for it. Give it 110% 100% of the time. But then some say "let go and let God." So is a happy medium the answer? I don't think so.
The poet Rumi wrote:
I don't know whether the union I want will come through my effort, or my giving up effort, or from something completely separate from anything I do or don't do.
Sounds like a Catch 22 but it's not.
Doctors say that too much of the same thing is bad. Too much fast living or too much slow living. What works is fluctuation. Like when you see an image of a radio wave going up and down a horizontal line. Have you hit a stretch in your life that has a lot of stress--you need a lot of recovery time. Have you been doing nothing, have no stress, well, that's not good either. You need to get moving, take some chances.
And then there's the not knowing part. That calls for faith. I believe if I give my life everything I've got, that there is something that is going to let me know when to pour it on and when to back off. And yes, it can be frustrating trusting that. I remember when people used to say they liked a "nice even keel" in their life, I would always say I liked a "nice even high."
But I've come to see that life is up and down, ebb and flow, give and take. So now when my faith directs me to pour it on I give it all I've got. When it tells me to back off, I chill. (And I used to feel guilty chilling.)
So the answer is to do both. Blast full speed ahead but then when you hear that still, small voice saying, chill, go ahead and guilt-free take it easy.
That is going to get you where you want to go as quickly as is possible.