Well, a sense of proportion for one things. And even more importantly in terms of actual expertise and knowledge, a balanced understanding of how certain situations are likely to play out - especially when they've happened before.
This is the context in which I'd see the Liberal Democrats' present coalition with the Conservatives.
Ephemera such as yesterday's 'Vince Cable hates Murdoch' debacle may come and go. But the lineaments of the situation remain the same: every Liberal cohabitation with the Conservatives has ended in a split.
In the 1880s, it was the Liberal Unionists, led by Joseph Chamberlain, who left over Irish Home Rule - an idea so farsighted it might just have avoided the Irish Civil War and Partition.
In 1916-22 David Lloyd George led a 'coalition' that eventually became a Conservative government in all but name, eventually booting out the mercurial Welshman and obliterating the Liberals at the polls in the subsequent General Election.
It was the 'National' Liberals in the 1930s, who joined a Conservative-dominated coalition after the economic crisis of 1929-31. They were finally absorbed by the Tories in the 1960s.
Read your history? Then the future's pretty clear I would have thought. The Liberal Democrats' leader is so cosy with the Prime Minister that he shares takeaways and household chores with him; Liberal Democrat Ministers, despite disagreeing with most of the government's agenda, follow his lead. But the party machinery is being captured by Lib Dem leftists - the Party Presidency and Deputy Leadership, for instance - just as it was in Mr Gladstone's long struggle with the Liberal Unionists over Ireland.
The result might well be the same: acrimony, split, electoral defeat.
