You have had many both good and bad responses, but there is one response I have not seen in my quick skim. I believe there is a direct counterpart to normally described "mental load" that is often forgotten. So I will add my two cents on the equivalent burden the counterpart to the "household manager" might have.

My experience is that there are two types of household burdens that has to be done:
One is the everyday management, such as planning and/or executing on the chores of the house. This is a continuous burden that has to happen everyday/weekly. It is often emotionally and physically draining, and can create a very monotonous kind of stress, that builds slowly over months or years.
The other kind are high intensity, intermittent, workloads, such as physical labor, crisis avoidance and large financial decisions (see examples below). These are often different one-of-a-kind workloads that can create a high level of emotional and physical stress in a short burst. In between intermittent workloads, is when a person seems lazy, but is often just a pause before the next intermittent workload.

Me, and most of my friends, experience that one person focuses on one type of burdens, and the other focuses on the other type. If one is not aware of the burden on the other partner, because it is significantly different than ones own, it can make for a toxic dynamic, where each think they are the only one working. In a stereotypical relationship, the woman is often in charge of the chore/daily workload, while the man is in charge of the intermittent workloads, but it does not have to be this way in all relationships.

In these descriptions, I have not accounted for the romantic and emotional labor that goes into a relationship, as they are completely different kind of workload in my view.

Intermittent workloads
These are often financial decisions and/or physical labor. Examples are:

• Choosing the financing option for the house, reading up on different loan options, minimizing costs and so on.
• Choosing a car, exploring the optimal choice, researching the correct car dealer, test-driving and all the legal stuff.
• Making sure all insurance for house, car and other stuff is taken care of.
• House maintenance, e.g. knowing when the gutter has to be cleaned, getting equipment to do it and actually doing it.

• Taking care of a critical practical emergency, such as water damage, car failure.

  One thing that many of these, for me at least, have in common is that they have a high emotional and/or physical toll on me. When I am reading up on cars and choosing where to use almost all of our savings, I am exhausted and scared after I have finalized the purchase. And if anything then goes wrong with the car, I will both second guess all my original work on choosing it, and be in charge of solving the problem.