Biggest mistake in poetry?

We all know some poets just struggle with there poetry... well, what mistake does most poets make that ruins (or, makes it unoriginal) their poems?

Examples can be:
Rhyming (excessively)
Common words
Common themes
Use of first, second third person etc.

I'm curious to know what you all think it may be. And if this is not clear (as I'm currently procrastinating study for the history of the cold war) just let me know, I'll rephrase.

Incorrect spelling and grammatical errors.

Mr. Pianoman

I think these all have something to do with a bad poet: (They're all a problem)

Grammatical errors.
Bad spelling.
Cliche topics.
Forced rhyming.
Over use of pronouns.

xTheEcstasyOfSuicidex

i totally agree with all of these especially to the FORCED rhyming part because it confines the person to a specific area that doesn't allow him or her to properly convey his or her feelings.

i think incorrect spelling or grammar is sometimes intentional as to enforce or better express a hidden aspect. after all, each poet has his own poet's license.

Nancy

I guess my worst mistake in poetry is using"I" a lot, which I also see almost everyone else use. It`s very common and doesn`t take anything away from the poem if it is written well.

My worst mistakes would probably be...getting of on the beat of them poem, or the rhyming....either that or choosing the same topic and finding that I end up using things from past poems I have written

i don't think there are mistakes in poetry, besides spelling err's. Poetry is an emotional expression, not a grammatical expression.

forced rhyming is a big one for me. also, when people switch back from first to second to third person and the switching has no relevance to the poem and is just due to lack of paying attention. just a pet peeve though.

Grammer is a big one for me. But I also hate when people just barely express the situation, because then we have absolutely no idea what they are trying to display.

Biggest mistake:

Not expressing one's self, and just writing poetry so they can have a slightest chance of getting recognized as a "famous" poet. I think poetry is meant as an art for and means of expression.