Sole earner with a desire to build a house

The example was cancer. Fits.

I personally, I have said it several times, consider BU [Berufsunfähigkeitsversicherung] mandatory for a sole earner. Of course, keep your eyes open when choosing insurance. And yes, it is quite expensive. But the risk of slipped discs, cancer, mental illnesses is real. I know, individual cases are actually bad examples, but I have a colleague who simply collapsed in his shower in his late 30s due to burnout. In my opinion, he was not under special pressure. For him personally, it was simply too much. Fortunately, he is a civil servant. There are almost always solutions for that. A friend of mine is now in his mid-20s with a slipped disc. He might have surgery in March.

Such cases can simply drive a family into ruin. Even the sickness benefit after 6 weeks is a severe cut. And that comes faster than you can look.

If you have no clue about the matter, then get advice. From a fee-based advisor. But no one wants to experience that because of 80€/month they drive their family into financial abyss. In addition to their then serious illness.

Simply don't build too expensive or at any cost. Then you won’t have the stress.

But if everyone here goes to the financial limit just so the apartment owner can't afford alloy wheels, then you must/shouldn't be surprised if things go wrong in case of emergency.

But nobody wants to hear that here...

You’ll manage.

Merry Christmas

was there a BU in both examples and if so, did it have to pay out?

Well, it does make a difference whether you are a roofer, baker, or application developer.

Aside from the comment, what do you mean by that?!

Until the disability insurance pays out, quite a lot has to happen; a significant portion of cases also end up in court.

It pays when you are occupationally disabled, as the name already says.
The respective definition and the accompanying scope for interpretation are contractually stipulated. There certainly are (cheap) policies whose "small print" can cause a lot of trouble (e.g., abstract reference or badly formulated health questions), but that does not make occupational disability insurance per se bad, just the specific policy... and you do not have to sign that.
Analogous to the example of house construction with a general contractor – just because some GCs use poor service descriptions and sneakily take advantage of the builders (and ultimately may also end up in court) does not mean that building with a GC as such should be vilified.

However, it is damn expensive and the risk is certainly debatable

What does "damn expensive" mean in this context? Sure, I wouldn’t want to pay the policy for a roofer in their late 30s either (especially relative to income), but for the predominantly present "desk workers" here, we are talking about contributions in the range of 100€.
Of course, risks, probabilities of occurrence, etc., can be hotly debated and a consensus will never be reached. Fortunately, most of us will never have to claim such insurance, and even for those unlucky ones who will, it might mostly be only for a manageable period, which could also have been bridged with corresponding cash reserves.

But the fact is also: with a construction loan and children in the background, the loss of the primary earner is potentially existentially threatening. In contrast stand saved contributions over the critical 20-year period equivalent to the value of a garage. For me personally, the effort and possible gain here are in no proportion that would justify gambling.

Everyone has to decide for themselves. For us, selling the house would not be existentially threatening at all. We have good equity in the building, so we are unlikely to end up in personal bankruptcy. In general, I do not feel that my existence is threatened by the absence of homeownership. That would be the case for me if we had to rely on government transfer payments. But by no means if we had to move from a house to a rental apartment. €100 per month would nearly double our insurance expenses. I call that expensive.