Almost never because you lack the gift. Seeing a stride is pattern recognition, and when it will not come there is usually a reason, and you can work out which one it is. These are the usual suspects. Each one has a feel to it and a fix.
Diagnose it by doing. Streyed shows you approach after approach on the website and tells you on each one whether you read it right, which shows where the recognition is strong and where it needs more repetition.
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.
Fix: Before you blame your eye, ask yourself whether the rhythm, balance and amount of ground covered are staying roughly the same from stride to stride. If they are not, that is the job, and the eye can wait.
It is much harder to read a fence when you are constantly having to create the canter. A horse that is responsive to the leg gives you a more stable rhythm to read from, because small adjustments can stay small instead of becoming last-second kicks. This is not about going faster. A horse can be quick and still behind the leg.
Fix: Test the reaction to the leg on the flat first: ask, get an answer, soften. Then jump from the canter that produces, rather than the one you have to keep restarting.
At first, many riders only recognise what is happening in the final one or two strides. By then the smooth options are gone, so even a correct read cannot help the horse much. The goal is not necessarily to name the exact take-off point from the turn, but to start recognising the developing pattern earlier.
Fix: Count down out loud to a pole, "three, two, one" on the final three strides. When that is easy, start from four, then five or six. The number you first see it from is the thing to move.
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. Looking down tends to make the rider react to the final stride instead of reading how the distance is developing.
Fix: Keep your eyes up and towards the fence rather than searching the floor for a take-off spot. Many riders find it helpful to focus around the centre of the fence while keeping the rest of the approach in their peripheral vision.
Sometimes the eye is not the problem. You recognise a reasonable distance, then worry that it is wrong and change the canter anyway. That can turn a good distance into a deep or long one and make you trust your eye even less next time.
Fix: Practise making a call and noticing whether you immediately accelerate, pull or chase afterwards. Someone on the ground can tell you. The aim is not to do nothing forever; it is to stop changing the answer just because you have become aware of it.
Seeing a stride gets harder when all your attention is being used elsewhere: staying on, controlling the horse, worrying about the fence or desperately trying to find a spot. Tension narrows attention and often makes riders stare rather than observe.
Fix: Lower the difficulty. Use poles or tiny fences, repeat the same track and give yourself only one job at a time.
Riders who seem to "just have an eye" have usually built up a huge library of approaches for their brain to compare against. A jumping session gives you perhaps thirty, and nobody can freeze the moment to show you what four out actually looked like. Once rhythm, responsiveness and where you are looking are reasonably consistent, repetition becomes a major part of improving the skill.
This is where off-horse practice becomes useful. The recognition part of the skill can be repeated far more often away from the horse, because you can watch approach after approach, make a decision and immediately find out whether you were right. Streyed gives you a schoolmaster called Napoleon on the website 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. Try Streyed free and see which parts of the visual skill are already strong and which need more repetition.
Start with the canter. If the rhythm is inconsistent or the horse is not responsive to the leg, fix that first. If the canter is reasonably repeatable, look at where your eyes are, how early you are making a judgement and whether you change the canter after you make one. If those pieces are sound, the answer may simply be more repetition.
The drills for each step are laid out in exercises to improve your eye for a stride.