It is so easy to get stuck, I had an instance earlier this week, when a work friend and I had a little scuffle (larking about).
Someone, watching this, said

I understand you teach martial Arts
.
Eager to show off, I took my colleague by the wrist in order to show my perfectly honed Kote Geish (devilish wrist bending technique). He promptly tensed his arm, blocking the effectiveness of the technique. Forgetting the requirement of not leading your oppenent where he dosn't want to go, it all ended up in an unseemly struggle.

Dosen't always work in practice, does it!

, says the onlooker, before wandering off.
Moral of the story, don't do aikido, unless you are prepared to be humbled on a regular basis.