Trial and error is the best teacher.
Trial and error in my opinion may not the best teacher. If it is, leave the dojo and invent a martial art by trial and error.
You have a teacher teach you because you might not have the opportunity like OSensei had in creating Aikido. Be it time, money, genius or era.
Similarly, a senior does not teach what he does not know. He only corrects what he knows to be wrong. If we let you practice a technique wrongly all the time, it would not work. If it does not work, the techniques jams, and we'll both be standing there doing nothing. Much better use of time would be for the senior to show the beginner the correct way when he gets stuck. That way senior learns by reemphasising, beginner learns hands on. By way of anology, if a beginner TKD guy spars against a senior. The senior must give chances to the beginner for him to learn something. Otherwise, the senior might not leave any openings and instead repeatedly kick the beginner to a pulp. No one learns anything there. If you still don't understand this, ask a strong senior to hold fast (no chance given) on you and see if you can perform a technique properly.
As Thalib says, be honest as uke or nage.