While experimentation, why do you think it is difficult to assign any affect seen to any single hormone?

As all the hormones are synergistic to each other in their functions. Thus, during experimentation, we can not judge whether, a particular effect is produced by a single hormone or many. For example
(i) Auxins help to initiate rooting in stem cuttings, (an application widely used for plant propagation.) Cytokinins also show the similar function of root formation. Auxins promote flowering, e.g., in pineapples. They also induce parthenocarpy, e.g., in tomatoes.
(ii) Both gibberellins and ethylene are synergistic to auxin in initiating flowering and for synchronising fruit set in pineapples.
(iii) Cytokinins and gibberellins help overcome the apical dominance and delay the process of leaf senescence.
(iv) On the other hand, ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. This shows that all hormones are synergistic to each other in their mode of action in plants.