There are a lot of factors that could lead a person to success. A person could be successful when, for example, he is diligent. But of course, that's not true to all. There are people who still fail though they are diligent. So probably a mixture of diligent and perseverance. Still, it's not applicable to all. On the other hand, there are people who succeed by the use of flattery. They tend to be sycophant. That is, they flatter a person with higher authority just to win their favor. What I'm trying to say here is that a person can succeed in his/her own knack. But not all people succeed in life by the use of flattery alone. Some, maybe? But definitely not all. Stereotyping is a major NO-NO.
Being successful requires consistency of hard work and motivation. Motivation comes from confidence of one self and a drive to continue for a specific goal. Confidence in one self isn't easy, as many people have insecurities and judge themselves negatively which can lead to low self esteem which is low confidence. Flattery can help boost confidence leading to a higher chance of suceeding.
I am living proof that flattery is not the key to success. I am successful because my work product succeeds all others in my line of work. I am actually not flattering to my supervisors as I make waves and force changes to make our company better when they would prefer the status quo. Flattery is unneccesary as long as your work product cannot be replaced.