I'm late to this party, but I appreciate what has been shared. I have been treated ruthlessly and so shrewd people make me feel uneasy. But when I look at the definitions, I think I've been wrong.
Ruthless - having no pity or compassion for others
Shrewd - having or showing sharp powers of judgment
Which of these was Rockefeller? He basically told competitors, "Let me buy you out or I'll bury you." If you refused, he would bribe your vendors and clients to drive your business under. (I say that as a historical fact; that's how he operated.) That's ruthless.
If you let him buy you out, you still "lost" your business but he would give you shares in his company and you could earn fairly good money. That's shrewd.
He was a very regular church-goer and insisted his children follow religious rules of honesty, etc. But the truth is, he was ruthless, not shrewd. He could have been shrewd and simply beaten his competitors honestly. Instead, he resorted to dishonesty to destroy his competitors. THAT is ruthless, according to the definition I see.
So as I compete, will I simply work harder and smarter (be shrewd)? Or will I do what it takes to harm and destroy my competitors (be ruthless)? The answer? Is the extra money worth showing that you cannot possibly win without harming other people? Not to me. That's my right to choose.