[DoughnutHole]

It's a residue of being historically a very poor country. There's no belief that hard work is for chumps - laziness is also looked upon very negatively. What we do have is no faith that hard work will lead to "success" or material wellbeing - hard work is what you just have to do to survive.

Until very recently the Irish historical experience has been that you work very hard your whole life and at best your children's conditions are the same as yours, at worst they deteriorate.

In this context it makes sense that bragging or boasting are looked upon very unfavourably. If everyone is working themselves to the bone to just barely survive, then "success" isn't so much a result of your moral superiority and work ethic as it is a result of dumb luck. In that context boasting is distasteful.