How should I word this part of sentence?

"Our mistakes are lessons learned if we don’t make them again, if we do it’s only human but they will take their toll on us. "

This is how I'd write that sentence-

Lessons are learned from our mistakes, when we don't make the same mistakes again. As humans, if we repeat the mistakes, then no lessons are learned, and can often take a toll on us.

However if you just want the last part changed, I would say-

"If we do, it will take a toll on us, we're only human"

Remember to talk in the same person, don't jump from first to third person.

Hope I helped!

I would say "Our mistakes are lessons learned if we don't make them again. If we do it's only human but, they may take a toll on us."

This might help:

http://www.grammarly.com/?q=grammar&gclid=CKbN4o_-...