I've realized that to succeed in meditation you have to practice continuously — but more importantly, when you find a calm thread, you have to hold on to it. Momentum is the key. This holding on to one small thread that worked is very important — if you keep holding that thread, it grows stronger and stronger. Lost momentum means starting again from scratch, and the drift can last days, months, or years. So it matters to practice every moment — not by gripping the calm, but by being willing to return to it again and again.
This asks for a different mental attitude. Rather than feeling "I am sad, and I am sad because this didn't happen," we investigate the mind to see why the sadness arises at all — what the actual source of that craving or aversion is. We learn to see the mind's play for what it is — like a toy that once held us completely, now just a thing we can set down — until its grip loosens and we no longer get pulled along. The aim is to clearly see the mind's own workings, and to hold the desire for a truly delightful mind within — one that depends on nothing outside itself.