A venerable client wrote recently and asked, "Should 'that' be added before 'innovation' in the following sentence?"
At our firm, we know innovation often results from hard work and long hours.
We took our answer from The Gregg Reference Manual:
As a subordinating conjunction, that links the dependent clause it introduces with the main clause. That is often omitted (but understood).
We realize that our bargaining position is not a strong one.
or: We realize our bargaining position is not a strong one.
However, under certain circumstances that should not be omitted:
When the word or phrase following that could be misread as the object of the verb in the main clause.
When that introduces two or more parallel clauses.
When an introductory or interrupting element comes between that and the subject of the dependent clause.
NOTE: If you are in doubt, do not omit that.