One should always be careful of falling victim to using and reusing forms because it may come back to bite you.  Many drafters of affidavits start out by having the affiant state something like, "I have personal knowledge of the facts set forth below."  This language by itself may not be sufficient to give anything

Beware of using "form" language in an affidavit to establish the affiant’s personal knowledge of the facts A statement such as "I have personal knowledge of the facts in this affidavit," may not be adequate.  And the danger of getting it wrong is that the affidavit is legally insufficient.  

A good discussion of how far an affiant must go to establish personal knowledge is found in the Houston Fourteenth Court of Appeals‘ opinion in Valenzuela v. State & County Mutual Fire Insurance Co.   The court of appeals held that a "mere recitation that the affidavit is based on personal knowledge is inadequate if the affidavit does not positively show a basis for the knowledge."  "The affidavit must explain how the affiant has personal knowledge." (emphasis added).

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