Labour can feel one of two ways.Organised. Or disorganised.
A body in birth needs to organise itself. When it has the chance to, contractions coordinate with breathtaking precision. They become so preternaturally powerful, no matter how many times one is in the presence of it, you just go, wow. How bloody clever is that? How in heaven does that happen every single time? The two-minute tempo ticking in time; the steadily building momentum; the progress and purpose so sound and sure. And all without a conscious thought from the mother herself.
And then there's the opposite of organised. The erratic a-rhythm of the body if it's interrupted - the halting, hesitant UN-flow of a labour that gets disarranged.
Sometimes it just is that way, a baby in a tricky position for example. A deep, unbudgeable fear. But what more usually throws a labour off, are little things. Not the adrenalin or obvious stress, that classes can sometimes talk of. But subtle disruptions, like being conspicuously timed or managed, feeling watched or evaluated; expectation, deadlines, discomfort. Stuff that, at first, just doesn't feel wrong, for the simple reason we've been taught to see it as normal.
So think carefully. Know what you need. Find a mother who had a more complicated birth than she expected to, and ask what got in her way. What stopped her body from concentrating?