Personally, I find ki to be something of a feeling.
The whole "being in harmony with your environment" thing.
I remember fully well the feeling it had.
Something like I could do everything I wanted with my opponent, I felt him out, I had control over him.
Somewhere, something completely connected him to me and left me in charge of the situation.
As long as I kept feeling and moving, in that particular state of mind, my opponent was no where.
And indeed, an aikido practitioner will have a hard time sparring due to the fact aikido does not give the possibility to spar or compete.
This is mostly due to the fact that the techniques are designed to sever joints and break bones.
Aikido uneffective? No. It's very effective and this comes at the expense of the option to build practical/combat experience.
It's unpractical, not uneffective.
An experienced fighter that has good knowledge of aikido is very much lethal.
