So what went wrong? After all the reasons have been listed, it would probably be a toss-up between Sonia Gandhi on the one hand and Dr Singh's innate decency on the other.
Politics and governance are not for moral people. Nor are they for the docile. Dr Singh suffered from both flaws. Beyond a point he would not defy Sonia Gandhi even when she was taking him, the economy and, at times, the country down the tube. But ask yourself: which Congress minister would have done that?
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In that sense, Dr Singh was not worse than anyone else in the Congress party, which has the highest per-square-inch density of poltroons in the world. But in every other sense, he was better - properly educated and with family values. Nothing much more needs to be said of a human being.
By contrast, his ministerial colleagues left a lot to be desired, most notably some very senior ones who never accepted that he was the boss. Many of them boasted about how they ignored him.
A junior minister once told me how during the first term of the United Progressive Alliance (UPA), two senior ministers from Bihar would keep talking to each other even after Dr Singh had taken his place in the Cabinet room.
He would wait for them to pay attention. That courteousness defines the man.
There was also the intolerable posturing of the Left, without whose support UPA I ran the risk of collapsing. Dr Singh once collectively referred to them as shaamat (Urdu for calamity).
So, as if having to deal with fools was not bad enough, there were knaves too.
MMS vs SG
In the end, though, he pulled off the impossible: he got the better of Sonia Gandhi with his Indo-US nuclear deal. And in that triumph perhaps lay the seeds of his eventual tragedy.
By choosing to overlook some completely inexcusable conduct on the part of his party and later of UPA allies, of which the cash-for-votes affair in July 2008 was only the first, he made his first mistake. Even so, given the moral ambivalence of politicians, he may have had a slower decline. However, that was not to be.
Most people think Dr Singh's problems began after the Comptroller and Auditor General's report on the 2G allocations. Actually, they started soon after the UPA resumed power because Sonia Gandhi thought it was time to take him down a peg or two.
She greased the pole for him, not least by letting it be known that her darling son - not widely known as the sharpest tool in the box - was born for one, and one, purpose only: to be India's prime minister. For the Congress party, that became another reason to ignore Dr Singh.
He should have resigned then, or perhaps after his bypass surgery in 2011. But for reasons known only to him, he chose to stay on. That, verily, was the biggest mistake of his career - because those who don't know when to quit, or decide to hang on even if they do, pay a big price. Their careers almost always end in tragedy.
Even the great Sachin Tendulkar was not an exception to this age-old rule. Nor has Dr Singh been one. More recently, L K Advani and Murli Manohar Joshi of the Bharatiya Janata Party, to name two of the latest victims of Moore's paradox about how people refuse to face facts, provide good examples. Both politics and sports discard losers with a disdain not seen in other professions.
"… we are underlings"
I once asked someone who knows about these things as to where, in his view, Dr Singh erred in the matter of governance. He thought for a long time and finally came out with his explanation: "He conceded too much ground to his ministers."
That is possibly perfect mot juste for Dr Singh's 10-year run. While this may have been understandable for UPA-I, it was inexcusable for UPA-II. He needed to have - and indeed could have - asserted himself far more.
Instead, he withdrew into a shell and forgot one of the most basic rules of politics, as enunciated by two economists called Allan Gibbard and Mark Satterthwaite. In a nutshell, the rule is that all democratic forms of government in the end have to become dictatorial because someone must take the call.
That is what all great leaders do. Dr Singh did it, too, though only in a manner of speaking because the call he took was for inaction, lest he upset the Sonia Gandhi intention that, come what may, UPA-II had to last the full term while Bonnie Prince Charlie made up his mind about becoming prime minister.
As he prepares to leave 7 Race Course Road, it is hard to say whom Dr Singh blames more for his predicament - himself or his stars. But as Cassius said to Brutus:
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."