I don’t think he was unlucky to be around at the same time of the other three - I doubt he’d have reached the standards he did, without their presence. Murray’s mental strengths lay mainly in the determination to succeed. When he failed he would always say he’d work harder and harder - perhaps he had to work smarter? Regarding ‘he never knew when he was beat’, I’d say it was the exact opposite. It was clear as day when Murray knew he was beat - body language and interaction with his team changed as if a switch was flicked.
He was also fortunate, imo, to have it portrayed as there being four players at the top of tennis, especially, when Wawrinka won just as many grand slams as Andy did. On the subject of Wawrinka, If I was Andy Murray, I’d be a bit fucked off at the realisation that I didn’t win any more grand slams than him.
Where he was unlucky, was meeting grand slam winners in his first grand slam finals - those finals taught him how to lose the biggest matches. He saw the guy on the other side being able to step up at the most important points and he couldn’t. The others faced non grand slam winners in their first finals, which was a huge advantage for them. If Murray had faced a player like Cilic or Wawrinka is his first grand slam final, he may have gone on and won more.
Overall, he was a fantastic, world class tennis player - the best we’ve ever had in this country.