You have to “let go”

In meditation practice you come to a point where you have to “let go.” It’s easy for me to do this at night, I’m usually tired and there isn’t any resistance, but it’s 1,000 times harder during the day. I’ve done it a few times for brief periods and the experience is really remarkable, but I haven’t been able to sustain it yet. No telling what happens when I can sustain it.