Rabbi Yisrael Lipkin of Salant
Like a bird, man can reach undreamed-of heights as long as he works his wings. Should he relax them for but one minute, however, he plummets downward.
From Tenuas HaMussar (The Mussar Movement)
Modern Uberdox
“I write not because I have the strength to write, but because I do not have the strength to remain silent.” -Rav Avraham Yitzchok Kook zt’l
Not unlike one of the comments on your cement mixer analogy!