This can often occur as a result of irrational fears apparent in one partner linked to jealousy in the past. (elitesingles.ie)
This is the same kind of irrational fear that causes parents to avoid vaccinations, opening them up to diseases that were all but wiped out hundreds of years ago. (momtricks.com)
I'd say a lack of skepticism at this level is actually a sign of irrational belief in the ability to predict what can't be predicted. (oilprice.com)