A banner in a local restaurant is a print of Mitsuo Aida's writing.

It says, "つまづいたっていいじゃないか にんげんだもの", all in hiragana. Still, it took me quite a while to figure it out, largely because of "du". The word in front is actually "tsumazuku", "to stumble". Ergo, "It were ok for me to stumble, I'm only human". Or something like that.

I don't have a foggiest idea when it is appropriate to use "du", so it's one of those mysteries.