Currently, I prefer to solve simple tactics. I often become frustrated when I try to solve difficult tactics and I can't. By solving simpler tactics I work on the basic elements of more complex ones.
I agree with you. Simple tactics are good enough to make us remember the motives. It is also easier to keep keep motivated. When we get better, the definition of "easy" and "difficult" change. At the moment I don't try difficult combinations, but rather basic exercises. I will train them so long until I know them rather well, and only then I with try more challenging combinations.
Currently, I prefer to solve simple tactics. I often become frustrated when I try to solve difficult tactics and I can't. By solving simpler tactics I work on the basic elements of more complex ones.