Sure.
Here's how I 'envision' it to be...
If you target a spell on a creature, which has a save, there is some sort of mental struggle or something similar when you try to penetrate the creature's defenses with the spell energy, which is why you notice, whether you succeed (win the struggle) or not (lose the struggle). Spell resistance would work in a similar way.
For effect spells, there is no such 'feedback', because there is no such 'struggle', you just fire the spell effect at the creature like a weapon.
In addition to that, there often might be visual effects, which hint about what happened, i.e. a rogue dodging an area blast completely is certainly noticeable.
Bye
Thanee