When the Stickies took over Labour, I knew it was destined to be a fringe party. On the other place, I kept saying that Labour was in trouble and that the decision to go into coalition with FG in 2011 was a massive strategic error. SF is about five years ahead of the curve in terms of where I thought it would be. Opinion polling is Astrology with a veneer of Numerology. (I work with large datasets of hundreds of millions of elements so I might be a bit biased when it comes to people prognosticating on the basis of samples of about 1K. The media analysis of these opinion polls, without understanding their serious limitations, often looks like children playing at being grownups. The Brexit and Trump threads on the other place were full of such people who were so convinced that Brexit wouldn't happen and Trump would never win because they did not understand how problematic and non-representative the opinion polls were even when it was explained with drool-proof electrons.) It is far more important to analyse why things happen and how they happen.Did you ever think you’d see the day that SF would have 10x the support of Labour in a poll.
Apart from the clientelism model that dominated a lot of Irish politics for decades, there is another factor that has a major effect. That's the incompetent school teacher's Dail sabbatical. These people are not really good at being teachers so they throw themselves into a political career because they have the free time and opportunity to meet more people than the average person. The other teachers are often happy to see the back of them and kids may get better teachers as a result.
The ideal situation for a party would be that its representatives have a wide range of expertise and backgrounds that continue to reflect society and its electorate. The general problem at the time that Labour started to decline was that teachers were over-represented as a group in the Oireachtas with approximately 26% of seats. Society changed but the parties did not. Throw in the whole generational thing of family seats and parties are facing a kind of toxic trio of clientelism, non-representative TDs and political inbreeding. Left unchecked, it overwhelms parties.
Society has become (allegedly) better educated in the last forty years or so and this meant that the Dail, and political parties, were, due to a lack of term limits, gradually becoming less representative of their electorates. When that happens, there is a time where the number of new voters a party gains is overtaken by the number voters that it loses. It isn't just a pattern of election ebb and flow. It is also the point where any mediocrity of its representatives becomes absolutely lethal. (Lenihan, Cowen, Noonan, Varadkar and Harris are good examples of people out of their depth having catastrophic impacts.) There's no new thinking and too few new candidates. The party becomes dominated by aging careerists who cannot adapt and are more concerned with keeping their own snouts in the public trough rather than growing their party. The problem for parties in that kind of electoral death spiral is that they lose relevance and their ability to survive as major players. It even affects larger parties. Labour got demolished. FF is also in trouble. FG nearly got overtaken by the PDs (Provisional FF). The PDs had a chance to replace FG but blew it. If SF does not continue to evolve with its electorate, and with society in general, then it will suffer the same fate as Labour.