can't develop courage, but you can desensitize fears. systema teaching/learning methodology revolves around that. they put you in lots of uncomfortable training situations and work with you to desensitize the fears which cause tensions in your body. personally, i think systema folks can teach aikido folks a number of things on relaxation and breathing.
here is an example. take a jo, slide it between your elbows and behind your back. now do forward front fall, then back fall, then forward roll, then backward roll. uncomfortable? fearful? you betcha! can it be done? you betcha! watch the backward roll out of the chair on this video http://www.youtube.com/watch?v=wLY68FBcCwo
how many aikido folks comfortable with their backward roll to try that?
ya, 'em buggers are crazy, but kinda fun to hang around.