It means he/she was not a person who accepted the second choice. He/she always wanted the best of everything. Here are some literary examples of " second best". " And when Anne, dressed in her second best, as primly opened it, both little girls shook hands as gravely as if they had never met before." Anne Of Green Gables by Lucy Montgomery. " She was wearing a black cashmere dress that had been her aunt Jane's second best." Rebecca Of Sunnybrook Farm by Kate Wiggin

One means "someone" in this context, and this would only work as a relative clause (ie. extra information). It can't stand alone as a sentence. Second best means you accept the second option instead of fighting for what you want. A "seven-figure mark" means the amount is in the millions. You're counting each numeral in the total amount (=seven).

yes, i am sure there is a "one".Thank you for your help. May i aks another one?What does "seven figure mark" mean?of course,it is in another sentence.

It depends on the context. It could mean I (he/she) have never been a person who accepts things that are not the best. The one refers to a person, probably the person who is speaking.

You sure there was a "one" (between "never" and "to") in the sentence? So do you understand what it means put "never to accept second best"? I guess your sentence would mean someone is so competitive that he would never be willing to be the second, but always to be the best. The "one" could mean "not once, not at all".