This a constant debate. When someone says 25k is enough I just don't believe it, but I know some poorer Thais have that kind of income and survive.. with unsustainable debts for most of them..
But the answer is in lifestyle. Before retiring I was in a mid level position in a UN agency in Geneva with some extra income from Israel. Altogether THB 500k after tax. This gave me a reasonable lifestyle, good holidays, good restaurants and nice activities like Paragliding, Scuba diving, mountaineering, hiking, skiing.. Family of 4, and I managed to make some savings, fortunately.
Here, with a new family of for I try to have the same lifestyle, without the "nice activities" because of age and "TIT". I have been spending all my 300k monthly pensions and denting my savings for the past 9 years. Everything I like is just so expensive. And don't ask, I have no interest in cars, modest Hondas fulfil our needs, Kids don't go to an International School and medical bills are refunded by my health cover.