[wickawic]

Explaining is usually more difficult than understanding, as well.

[southpawflo]

I've had multiple teachers tell me that if you can't explain something you don't completely understand it yet. grok what I'm saying? :)

[nostalgiac]

I've heard this a few times but thoroughly disagree.

Being able to explain/teach something to others is a very different skill to understanding it and isn't compulsory.