Labour history can provide some useful perspectives. The 2019 electoral defeat needs to be seen as part of a larger crisis of social democracy of long standing (and which has strong global dimensions). Labour has been electorally in decline since its high point in 1951 (ironically in an election it lost) when it got 48.8% of the vote. In terms of winning elections, Labour has never been very successful. The hundred years after 1918 were characterised by the electoral success of the Conservative Party. Long periods of Conservative rule have not been unusual in modern British history. This was why New Labour operated in the way it did: negotiating reforms in a conservative political culture and trying not to frighten the Daily Mail.
Labour has, however, renewed itself in the past and come back from the political wilderness:
Labour has renewed itself and won elections when electors viewed it not as a movement of ideologues but of men and women developing common-sensical and pragmatic solutions to the problems of modern Britain. Historically, the Labour party and labour movement more generally has been unperturbed by theory (to the annoyance of left wing intellectuals). It has won through providing realistic alternatives that could enhance everyday experience: the connecting thread in 1945, 1964, 1974 and 1997. It cannot simply rely on the Conservatives making mistakes. We know from the elections of 1992 and 2015 that the Tories can win even when they are not particularly popular. Labour historically wins when it is able to construct enduring coalitions of voters. Although the party has been based on the working-class vote (a complex and shifting set of electors), it wins when it addresses the nation as a whole.
It does not win when it is divided (the great problem in both the 1950s and the 1980s). Labour divisions have an almost cosmic dimension as both sides believe they represent the soul of the party. This makes Labour hatreds of each other so much greater than the Conservative equivalent: there seems to be so much more at stake. It also makes rethinking, and hence renewal, more difficult.
[Images: Tony Blair in 2002, source: wikimedia, author: LSE Library - taken from Flickr's The Commons; Jeremy Corbyn, source: wikimedia, photograph by Chris McAndrew, licensed under Creative Commons Attribution 3.0 Unported; Neil Kinnock conceding the 1992 General Election (with Glenys Kinnock and Bryan Gould), source: Wikimedia, photograph by John Chapman, licensed under Creative Commons Attribution-Share Alike 2.0 Generic; Clement Attlee, source: wikimedia, photograph by Winterbergen, licensed under Creative Commons CC0 1.0 Universal Public Domain Dedication; Photograph taken at the birthday memorial for Jo Cox, MP, at London's Trafalgar Square. source: wikimedia, photograph by Garry Knight, licensed under Creative Commons CC0 1.0 Universal Public Domain Dedication; Barack Obama at the Kohl Center 2008, source: wikimedia, photograph by WisPolitics.com, licensed under Creative Commons Attribution-Share Alike 2.0 Generic.]