Most people miss opportunity.
Opportunity is missed by most people.
The second statement is a restatement of the first, as a passive voice construction; you can also understand the second statement to be a simple predicate in which "missed by most people" is a complement applied to Opportunity, the subject.
Learning grammatical concepts and learning to understand and speak a language are often very different things.
It (opportunity) is dressed in overalls (clothing for physical work where the worker gets dirty).
Opportunity dresses itself in overalls. Or perhaps Opportunity is a little child and Opportunity's mother has dressed it in overalls.
Opportunity is dressed in overalls.
"dressed in overalls" is a complement applied to opportunity.
(It) opportunity looks like work.
The verb there is "looks like" or "looks", take your pick. The complement is either "like work" or "work". Opportunity resembles work.
It appears to be work.
Most people miss opportunity because they're expecting it to be something other than hard work.
"To miss" can mean "to fail to be in the right place at the right time".
He missed the train.
He missed an opportunity to get a free update to Windows 10. Perhaps he seized the opportunity to stick with Windows 7. :)
It can also mean "to overlook, to fail to recognize, to fail to notice".
I missed you standing there in the shadows.
Did he really say those words in the murder scene? I totally missed that.
So the statement is a bit of a pun or a play on words. We miss opportunity (as we miss a train) because we fail to recognize it when we see it. We're looking for something flashy, but opportunity is dressed for hard work.