Seems it turned out to be true for your MIL, didn't it? I think that saying is true for the most part but there are exceptions to everything. If your problems or lets say "our illness" doesn't over ride the "normal" part of us, we can affort to smile at the world. But I think most of us with depression have to be careful how many frowns we try to turn upside down.
<font color=blue>"Our doubts are traitors and make us lose the good we oft might win by fearing to attempt" --Shakespeare</font color=blue>
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Psalm 119:105 Thy word is a lamp unto my feet, and a light unto my path.