A good teacher with enough knowledge and experience can be rewarding. Even so, the maxim of 'Those who can't do, teach' also holds true. There are many Aikido teachers who cannot 'do' Aikido. The simple reason being Aikido is such a complex art. It cannot be described as science such as Maths where 1+1=2. In Aikido, there are basics which any competent Aikidoka would be able to show; and beyond those more complicated techniques that experience Aikidokas will be able to perform such as Counter techniques, Changing techniques, Variations, Weapons etc. Beyond that, is the essence of Aikido.
After all, what makes Aikido so different than other grappling arts? Jujitsu and Judo all rely on unbalancing the opponent and utilising the opponent's strength and power. Even striking arts are more devastating when timed against an opponents movement and direction. 1 hit knockouts occur not because your strike is suddenly more powerful, but because you striked at the right place and at the right time.
To understand this, we have to look at the meaning of Aiki. Simply said, Aiki is the harmonising or blending of power. If we can learn how to achieve this, we will have reached an advance level of Aikido. There are many levels of Aiki to be achieved, but even reaching Aiki-musubi or physical blending is a difficult process without a good teacher.
The other part of the equation is of course the Student. However good a teacher is, how well you learn something depends on how enthusiastic you are about it. If you train in earnest, your 1 hours work might equal anothers 5 days work. The important thing is to never lose sight of your goals and aspirations.
Learning an art is never an end to itself. The art becomes you and you become the art. Until we realise this, we will forever remain a mediocre student.