Learn English – When to use “be worth VERBing” and when to use “be worthy VERBing”

They are kind of synonyms but not really interchangeable.

To finish means simply bringing something (a task or activity) to an end, or simply stop doing it:

We finished eating our meal.
_{(In this case you wouldn't use complete: "We completed eating our meal." is not the preferred usage).}

To complete means finish making or doing, such as in:

He completed his Ph.D. in 1983.

But another meaning peculiar to "complete" is making something whole or perfect, or with the meaning of "filling a form"::

• He only needed one thing to complete his happiness.
• Please complete the attached forms.

While to finish means merely bringing something to an end, or stop doing that something, to complete has the acception of fulfilling something.

Lastly, I'll leave you with this I found on the net:

"When you marry the right person, you're complete. When you marry the wrong one, you're finished."

There is good discussion of the semantic differences in other answers, but the most important practical difference is that ignorant is a very insulting word that you should be careful about using, whereas naïve is not such.

In general naïve makes me picture a hopeful child who has unrealistic dreams and has not thought about the real world enough, whereas ignorant makes me picture a dumb, racist old man who won’t change his worldview in the face of overwhelming evidence.

So, for instance:

1. “I think you are being naïve, because...” is appropriate way to disagree with someone's theory at, say, a business meeting. It’s still a strong thing to say, and possibly condescending or belittling of your colleague’s theory.

2. On the other hand, “I think you are being ignorant, because...” is quite rude and aggressive. It's not practically very different from saying stupid even though the semantics differ.