I think the difference between your dad and the mechanic and most interpersonal relationships — including marriage — is that those two had a mutual respect for each other and both worked like hell from Day 1 to do their very best for the project AND for each other.
When it was necessary to rebuild, there was no question they would both do whatever it took, that they would both sacrifice any and everything to make it work — including the time and money and pride to admit failure and start over from scratch.
Most people aren’t willing to do that — and it’s even less likely that two people are BOTH willing to do that at the same time (in the same relationship). One reason people can get divorced and remarried the same day — or in a short timeframe — is that they had a friend who was putting in the work their spouse was unwilling to do.
On the other hand, many simply decide “I can do bad all by myself.” They’d rather figure out it all out on their own than with an bad or oblivious partner.
Of course, the other obvious difference is that BOTH people in this “couple” we’re experts to begin with.
How many of us start out in marriage and other relationships as experts?
How often does it happen that BOTH people in a relationship are experts?
And how often does it happen that BOTH experts have the humility to acknowledge failure AND the patience to start over?
Of course, we already know the answer — it happens less often than divorce.