Almost never because you lack the gift. Seeing a stride is pattern recognition, and when it will not come there is usually a specific, fixable reason. These are the usual suspects, in the order we would check them.
Diagnose it by doing. Streyed shows you approach after approach in your browser and tells you on each one whether you read it right, which finds the problem faster than any paragraph.
Try it freeThis is the big one. A distance is what the current rhythm will produce at the fence, so an uneven canter makes every distance a moving target: the answer changes with every stride, and no eye can read a question that keeps rewriting itself. A canter that builds on the approach eats the ground and presents the long one again and again; a canter that dies behind your leg leaves the horse chipping in. Before you blame your eye, ask whether the canter you are reading from is the same canter two strides running.
Seeing a stride is far easier on a horse that is genuinely in front of the leg, because a forward horse shrinks your decisions to almost nothing. He is already going, so you either sit quietly and wait for the stride, add a fraction because the engine is running anyway, or sit up and ask him to wait a fraction. On a horse that is not taking you, every distance has to be manufactured from scratch, and no eye can rescue that. Forward first; then the stride starts to see itself.
Experienced riders recognise the distance from the turn or several strides out. If your eye only wakes up two strides from the fence, the reading is not the problem; the timing is. By then the smooth options are gone, so even a correct read cannot help the horse much. Train earliness on purpose: count down out loud starting from three out, then four, then from the turn.
Hunting the take-off spot on the floor feels diligent and works against you, because the spot only becomes readable when it is nearly too late. Look at the middle of the top pole, and nothing else, from as far out as the turn. It is much harder to judge a target you are not looking at; let everything else stay peripheral and the distance reveals itself against the fence.
The riders who "just have an eye" are mostly the ones who have seen tens of thousands of approaches. A jumping session gives you perhaps thirty, and nobody can freeze the moment to show you what four out actually looked like. If your basics are honest and the eye still is not coming, the missing ingredient is nearly always volume, not talent.
That is the part you can train without a horse. Streyed gives you a schoolmaster called Napoleon in your browser and hundreds of scored approaches an hour: call the distance good or off, press when he is exactly the named strides out, read the lines that do not walk clean. Start with a free day and find out which of the five it is.
Rhythm, always. Then whether he is taking you, then earliness, then where you look, then volume. Work down the list in that order and most "I have no eye" cases resolve themselves; the exercises for each step are laid out in exercises to improve your eye for a stride.