Transport Minister Lui Tuck Yew's shock announcement yesterday that he was leaving politics after only nine years - four years as a full minister - was all the more puzzling for the lack of a reason.
Whether in his letter to Prime Minister Lee Hsien Loong or in his interview with Lianhe Zaobao yesterday, Mr Lui, 53, never directly addresses why he is stepping down at the next election in the prime of his career and life - becoming the shortest-serving minister here in recent history.
The only clue to Mr Lui's reasoning is in the second paragraph of his letter to PM Lee, where he writes:
"You and several senior members of the Cabinet tried hard to persuade me to change my mind. You reminded me that the responsibility of Government was a collective one, and no minister carried difficult problems like public transport alone."
Ultimately, Mr Lui seems to have decided that some things were his alone to bear.
In the vacuum of information at this early stage, theories have swirled that Mr Lui chose to quit rather than lose his seat at the next election, or that he was made to carry the can on this politically toxic issue for the People's Action Party (PAP).
But it is unlikely that helming a difficult portfolio would have cost Mr Lui his seat. After all, former ministers who oversaw unpopular policies in housing and population did not fail to be re-elected in 2011. And that when public sentiment towards the PAP was, arguably, more hostile than it is now.
It is undeniable that public transport remains an issue from the 2011 election where public sentiment remains broadly negative, in contrast to the gains in housing or immigration policy.
While the overall number of breakdowns has dropped, bus congestion has been eased and additional infrastructure is coming on stream, crisis situations such as last month's MRT power fault entrench a view of the system as deeply flawed.
Those who think that Mr Lui was made a political scapegoat say his decision not to contest again was designed to mollify the public, and to convince them the Government was holding someone to account over the transport situation.
But he has not been responsible for any kind of mistake. If there has been a failing, it is in not being able to improve the system fast enough - and four years is a very short time in transport infrastructure.
In any case, there are few voters myopic enough to attribute the problems of a system to one man, who took on the job only four years ago. There is also the incongruity of holding a government employee to account for what are, effectively, the failings of privately run transport operators.
It seems more likely Mr Lui made the decision entirely on his own.
Perhaps it is a self-sacrificial attempt to draw the sting from a politically toxic issue for his party and colleagues. Perhaps he was too discouraged by brickbats from the public, too tired of a thankless job.
The portfolio had the same effect on his predecessor, Mr Raymond Lim, who asked to leave the Cabinet in 2011 after helming transport for five years. He was 51 years old.
The transport portfolio seems to be a graveyard for ministers, cutting short promising political careers with its challenges.
Mr Lui's impending departure is the abrupt dimming of one of the brightest stars of the 2006 batch of PAP MPs, a group that includes Second Minister for Foreign Affairs and the Environment and Water Resources Grace Fu, and Second Minister for Home Affairs and Foreign Affairs Masagos Zulkifli.
Ms Fu and Mr Masagos are potential replacements if re-elected as they are among three ministers without their own portfolios in the Cabinet.
Or perhaps the buck might be passed to a new minister, one of the high-fliers likely to enter politics in the coming polls.
The question of why Mr Lui quit will, in time, fade into history.
The question that matters now is how to address the vexing issue of transport before it devours another promising political career.
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