You can only manage to avoid a tsunami by standing above it on a small stool if you are very graceful. If you aren't graceful enough the tsunami will knock you and the stool over and you'll be swept away like everyone else.
No matter how graceful you are, the still tsunami shook (しゅく) the small stool. That's where your gracefulness came in. The stool shook, but you didn't. You balanced yourself and refused to go down.