Yellow leaves in tomato plants?

It might be overwatering!  I let up on watering these tomato plants and within a couple weeks they recovered.

This experience reminded me of my repeated failure with cilantro.  Not only did I learn from those mistakes, but also I learned so much from visitors after sharing my struggles on this blog.        

What have YOU learned from a garden mistake lately?

"Learning starts with failure;
the first failure 
is the beginning of education." 

- John Hersey