Why is it difficult to recognize finger print?

[AC Question]

I have found that, it is difficult to recognize my finger print on my samsung mobiles ( s5 , s6 edge) .
May be i cannot produce the right type of finer prints every time i touch the mobiles or the software is not versatile enough to recognize the difference of my touches on the mobiles?

 

[belodion]

I believe that there is a particular method of using the Samsung fingerprint sensor, is there not? A straight downward swipe of the finger pad across the home button?